In case you haven't noticed, vintage is hot right now. Vinyl records are making a comeback, vintage clothing stores are booming, and midcentury (1950s and '60s) decor is all the rage (see "Mad Men" on TV).

But vintage geek is even hotter than vintage chic. How do I know? I run a site called The Collectors Weekly, which aggregates the best the Web has to offer in more than 500 antique and vintage categories -- the best expert advice, the best informational Web sites, and the top eBay auctions.

So here's my top geek gift picks for this holiday season in vintage computers, LED watches, slide rules, and calculators. Each link below will take you to a section on my site listing actual items for sale. But be careful: Vintage geek is highly addictive.

Vintage personal computers
Remember that old Mac SE you had? The PC XT you bought despite the Charlie Chaplin ads? Your TRS "Trash" 80 with optional tape storage and 300-baud modem? Not trash anymore, my friend -- they're vintage!

While many of the earliest, prototypical computers (such as the original 1965 DEC PDP-8) ended up in the hands of Microsoft billionaires or institutions like the Computer History Museum, there are still plenty of gems floating around garage sales, online auctions, surplus equipment sales, and maybe your friendly neighborhood dumpster.

[ Know someone who waxes nostalgic over Silicon Valley's early years? Then check out the author's aggregate listings of vintage personal computers on sale now. ]

Keep your eyes open; the secret is knowing how to separate the junk from the treasure. As with many antique and vintage items, displayability is key. With vintage PCs, that means it's in good working condition and has all its accessories. And most important, it looks good in your living room, so you can show it off to your friends.

As I write this, the high bid on a 128KB Mac on eBay is $308, and it'll go higher before it ends. That's because it's the full package: a systems disc dated 1984, Mac Write, Mac Paint, an ImageWriter (with manual and case), an external floppy, the original mouse and keyboard, and no burn-in on the monitor. By comparison, you'd be hard-pressed to sell a nonworking early Mac without any trimmings for $50. That's a doorstop.

Rarity is another factor in vintage PC valuation. The IBM PC (Model 5150, 1981) and the Apple Macintosh (128KB, 1984) were the first large-scale production PCs. Other, lower-volume machines from that era or before can be hard to find in pristine working condition. MITS Altair 8800 (1975) and 680 (1976) kit computers, Apple IIs with low serial numbers (1977), early Commodore 64s (1982), and Apple Lisas (1983) -- all these rare birds can run you up to $1,000. An extreme example: Apple 1 boards, of which only 200 were sold, have sold in the five figures.

If none of the above appeals to you, there are plenty of other vintage PC names to chase: Compaq, Kaypro, Amiga, Sinclair, Franklin, Xerox, Digital Equipment, Atari, Heathkit, or Texas Instruments. Maybe something in an early Silicon Graphics? A PS/2 with Microchannel? Vintage magnetic core memory? A working IBM AT could be a real "get" for your collection. And come to think of it, don't throw away that original ThinkPad 700 (1992).

Finally, keep your eye out for vintage computer-related paper items or, as we say in the trade, "ephemera." Some early magazines, like the famous January 1975 Popular Electronics featuring the Altair 8800, can fetch more than $100. And at Christie's now-famous 2005 "Origins of Cyberspace" auction, a 1929 IBM maintenance manual, "Care and Adjustment of Electric Tabulating Machines," sold for $840. Who says you shouldn't keep those old manuals?

Vintage 1970s LED watches
In 1972 the Hamilton Watch Company launched the Pulsar P1, the first ever digital watch, utilizing low-current CMOS technology to show the time in a simple display of red digits. According to the lead engineer on the project, they were inspired by the futuristic digital clock in the 1968 movie, "2001: A Space Odyssey."

These 18k gold units (original retail price: $2,100) are the Holy Grail of vintage LED watch collecting. The 30 or so examples known to exist trade for $5,000 to $10,000, depending on condition, completeness (original box), and documentation. In fact, a circuit board for a 1969 Pulsar Hamilton Prototype recently sold for $12,000 on eBay.

[ Rolex? Movado? They can't hold a candle to a Compu Chron. Check out real-time listings of genuine 1970s LED watches. ]

Also on the high end are early LED calculator watches that included a numeric keypad, like the 1977 Pulsar 3822 or the 1977 Hewlett-Packard HP-01, which can each command several thousand dollars in pristine condition. Expect to pay up to $1,000 for other early LED watches from Pulsar, Bulova, MIDO (Swissonic), Timex, Texas Instruments, HP, Compu Chron, and Omega. Models with green displays are particularly rare and command high prices.

In the midrange ($100 to $400) are popular models like the Pulsar P2, famously worn by Roger Moore in the 1973 Bond movie "Live and Let Die." These are more widely available; pricing depends upon condition. On the very low end, if you just want to recapture the sensation of turning off the lights and pressing the button to see the time shown in red (LEDs drew too much power to leave them always on), there are plenty of other LED watches available for less than $100.

LED watches were ultimately replaced by more efficient always-on LCDs in the mid-1970s, when Texas Instruments introduced a mass-produced model for only $20, soon followed by Seiko, Casio, and others. People collect these too, but it's not the same geek experience.

Vintage slide rules
Though invented in the 1600s by William Oughtred, mechanical slide rules didn't really peak until the 1950s and '60s, just before the birth of the electronic calculator. In the wake of the surprise 1957 Russian Sputnik launch, America spawned a generation of engineers, all carrying this indispensable tool. (To see slide rules in action, just watch the movie "Apollo 13" -- they're ubiquitous.)

[ Long before the computer, the slide rule was the ultimate geek accessory. Check out the wide range; some are genuine antiques. ]

The rarest slide rules are 19th-century hand-engraved instruments such as Palmers Computing Scale (a circular model), first published in 1843, or the cylindrical Thacher's Patent Calculating Instrument slide rules produced by Keuffel and Esser in the 1880s. These can run close to $1,000 and are fragile antiques (taking them down to the track to calculate odds on the next race is not advised).

On the other hand, for less than $100 each, you can buy an almost limitless variety of very cool mass-produced 20th-century slide rules from companies like K&E, Pickett, Gilson, Dietzgen, Post (which became Teledyne), Faber-Castell, Aristo, and more. Veteran collectors tend to focus on obscure rarities, but I'd recommend just buying what you like.

Some collectors focus on private-branded models (slide rules that say "NASA," "Los Alamos National Labs," or "IBM" on them instead of the manufacturer's name). Others prefer intricate and colorful circular slide rules, or the original mahogany and celluloid slide rules of the early 20th century (later models were metal and plastic).

Whatever you do, be sure the slide rule is intact and working, since finding replacement parts for a specific model (especially the cursor, which moves up and down the device) is next to impossible.

Vintage calculators
You may already own a vintage calculator from the 1970s or '80s. People of a certain age tend to have an HP 12C, 10B, 59, 67, 45, 21, 38, or some other number hanging around in a drawer somewhere -- and a select few of those might even be worth something. An original HP-25 programmable calculator (made from 1975 to 1978) in great condition with all the trimmings will bring you about $100 on eBay. But for the most part, pockets electronic calculators are a dime a dozen.

[ Electroniccalculators from the '70s are fun, but you'll get even more enjoyment crunching numbers on mechanical calculators that actually make a crunching noise. ]

The richer (and geekier) vein to explore here is mechanical calculators, whose run started in the 1800s with Charles Babbage's proposed "difference engine" and lasted through the 1960s. Mechanical calculators were produced in large volumes for business users, beginning in the 1880s with the now collectible Comptometers and Burroughs adding calculators.

But the truly educated vintage geek will want a cylindrical mechanical calculator made by Curta in the late 1940s (Type I) or mid-1950s (Type II). Designed in a WW2 concentration camp by entrepreneur Curt Herzstark and made in Liechtenstein, only about 140,000 of these compact devices were produced. They were the first truly handheld calculator, utilizing a stepped-gear calculating mechanism. Popular at the time with land surveyors and sports car rally spectators, these beauties today command close to $1,000 in good condition on eBay and elsewhere.

Of course, if you're just looking to show off a vintage calculating device without spending big bucks, I'd suggest the Little Professor calculator game, introduced in 1976 by Texas Instruments, complete with red LEDs. Instead of typing in problems, you type in the answers -- but for $25 on eBay, who cares? It's classic vintage geek.

If these suggestions have whetted your appetite, they're just a start. This is a long-tail market if there ever was one, so there are literally thousands of vintage geek items to collect and become an expert on. What's more, there's tons of detailed information on the Web for almost every one of them, so it's easy to get sucked in.

So happy shopping, and next time you're at a garage sale or flea market and see a pile of old electronics, take a closer look. There might be a treasure in there!