In this day of the weekend yard or garage sale, we've all learned that what is junk to us may be glorious to someone else. And they're even willing to pay for it.

But often overlooked as other customers for your closet and attic clutter are the nation's collectors of practically anything you can imagine.

For example:

* Old TV Guides. Jeffrey M. Kadet, 34, of Rockville has shelves filled with at least one copy each of the more than 1,490 weekly editions published since 1953, and is still buying the older ones. "I grew up in front of the TV set," says the University of Maryland psychology graduate who makes his living selling duplicates. (To Howdy Doody freaks, for example, whose collections would not be complete without the magazine's Howdy Doody cover.)

* Water pistols. Jean Hall, 34, of Rockville was "bitten" by the collecting bug 10 years ago when she spotted an elephant-shaped plastic pistol in a gift shop. "It was terrific. It had jeweled eyes. I bought it on impulse." She's still buying, has "hundreds" in her home (the oldest dating from 1896), and hopes to do a book on them someday.

* Old toy banks. When Ralph Berman, 73, of Annandale, retired from the Treasury Department 12 years ago, a friend suggested a hobby collecting non-mechanical, cast-iron banks. "Like most collectors, I searched the family hideouts first." Now he prowls antique shops and auctions seeking acquisitions to add to the several hundred he already owns.

* Cigar boxes. "Nobody in the world knows as much about cigar boxes," boasts Henry A. Hyman, 42, of Watkins Glen, N.Y., who has more than 4,000, many dating back a century or more. "I started at 12. I was a very poor kid, and they were free." Impressed by their "incredible visual beauty," he's still buying one or two a week.

Aware that money can be made from selling to collectors, Hyman surveyed 4,200, winnowed their names down to about 500 willing to buy by mail, and published the list in The Where to Sell Anything and Everything Book (World Almanac, $7.95, 400 pages). Kadet, Hall and Berman are among a number of Washington-area collectors included.

What else are collectors looking for? Name it:

Children's lunchboxes, automatic sprinkler heads, unusual spark plugs, antique erotica, London street name signs, cheerleader memorabilia, unusual barbed wire, early Mad magazines, scenic postcards of Oklahoma and Kansas, pre-1940 animal license tags, or "anything" connected with McDonald's hamburger stands before 1975, "from the golden arches on down."

"Most items sought by collectors sell for $5 to $50," says Hyman, "but that's a lot of money when you consider how easily some of these everyday items might have been discarded as valueless."

To make money on them, he says, you don't have to own them yourself originally. You may spot an object going for pennies at a local garage sale, buy it on speculation and resell it at profit to a collector across the country.

Hyman, for example, keeps alert for old sewing machines. He recently saw an 1868 Singer priced at $50 in an antique store. "I went home, called a collector I know in the South, and offered him the machine for $200. He was delighted, and we made the deal."

To be successful, however, you have to "develop an eye for a fine item" and be aware of what collectors are searching for. "You take some of those weird things -- darn few people know about them. It's a godsend if you become even moderately knowledgeable to snap up a good item."

Generally, collectors tell him, the most desirable objects are "old, colorful, unusual and in mint condition." Condition probably is the most important quality. "Collectors don't want cups without handles. If you've got junk, throw it away."

And don't expect collectors like Kadet or Hall to buy just any TV Guide or water pistol. Kadet prefers to buy magazines in a series, if perhaps -- as he did -- you saved several years' worth as a child. (He stacked up TV Guides from 1955 to 1957, but "my parents made me throw them out. They weren't worth anything. On my 30th birthday, it just hit me. I'd like to try getting a complete set someday.")

For a series that appeared from 1953 to 1959, Kadet will pay $1 each. For those published in the '60s, it's 50 cents. He also is hunting for pre-1953 television magazines published in a number of U.S. cities. When he resells a TV Guide to specialty collectors, he may charge as much as $15, as he did for a 1954 Frank Sinatra cover bought by a fan.

Adds Hall of her water pistols: "It gets harder and harder to find ones I don't have." She has added about 10 so far this year. While she usually buys fairly cheap models, she once couldn't resist a $100 futuristic 1936 Buck Rogers model. "There are a lot of Buck Rogers collectors."

There are also a lot of toy bank collectors, says Berman, so the price can range from $2 to as much as $2,000. Unusual mechanical banks may bring thousands more.

The highest Hyman has paid for a cigar box is $125, though he has seen an occasional one go for $1,000 at auction. Most are worth $1 or less, although many could bring $5 to $45.

He estimates as many as 2 million different kinds of cigar boxes, which means his collection is far from complete. Years ago, he says, small manufacturers "created brand names more casually." Smokers could order their own brand, or they would be named after a hero of the day, or even a winning race horse.

Hyman keeps most of his 4,000 stored and cataloged, bringing out only 300 to 400 at a time to display on "the upper 2 feet" of his study. He usually picks a motif for the exhibit: "Trains, sports, naked ladies."

That collecting is big business is illustrated by the fact, he says, that there are more than 350 specialty publications for collectors of such items as dollhouses, Coca-Cola objects, cigar bands and prison memorabilia.

The next time you venture into your basement, don't overlook the potential value in those childhood "Uncle Wiggly" books, View-Master reels from 1939 to 1970, photos of female impersonators, political buttons from the Vietnam war period or early Cracker Jack prizes.

Somebody may want to buy them.