Coins. Mostly Silver. Some gold.
Science fiction. The great indexing project had completed the paperbacks, and I have just over 2300, with the hardbacks and the magazines (and I have lots of magazines) uncounted. I’m guessing I’ve got about 6,000.
Also, 3d jigsaw puzzles, and 2d jigsaw puzzles with maps and pictures of NY - though those sit in boxes, and I’m not sure I’d count them as a real collection.
Gee, this makes my collection of dogeared SK paperbacks interspersed with the occasional ratty SK hardcover look a bit sick…
Sewing thread, and not on purpose. I always think I don’t have just that one green, say, from among the hundreds of colors available, and when I get home, of course I have at least one spool of that green, if not two from the last two times I thought I needed it.
Vintage baseball and football cards. I’d guess I’ve got a couple of thousand, ranging from 1887 to 1965. I’ve been doing this since I was about ten years old. No way could I afford to buy some of these cards today.
Indian (Native American) artifacts. I’ve got several hundred arrow points, pottery shards, plows, etc.
Insects. My wife says that they make great souvenirs of the places we’ve visited. 
I just need to be a little better about keeping the collection organized.
Various comics, but in an intermittent fashion.
We have lots of books, but for some reason I never think of them as a collection.
Enemies. 
I would just like to say that that sounds very cool. There must be quite a nice aesthetic effect from the different colors, consistencies, etc. next to one another.
I recently sold a Marvin mug on Ebay for over $41, I paid 29¢ for it at Goodwill. I didn’t realize it was that collectible.
Stamps from all over the world. ( in a cardboard box in my closet she says quietly listening for some philatelic nerd boy to tut-tut.)
**Postcards ** from our travels. ( in a drawer)
Reference books on various thingies. ( animals, fossils, insects, trees…)
Loads of British Castles and Manor Homes stuff. more of an obsession, really.
Maps.
Vintage Evening bags ( only four, but I think they are cute.)
Purses ( Which will be sold on ebay this fall because it is time to break my addiction to these things.)
**Knitting paraphenalia. ** I have accumulated an obsene amount of knitting needles and books and yarn. Lovely, lovely yarn! in a very short amount of time. I’m not sure how this happened, but I cannot seem to stop myself.
Children’s books. Picture and chapter books. I don’t have enough shelving space for them, so they are piled neatly in my office. I have enough to fill up a modest country library. I really should offload them on ebay or donate them to some shelter.
Floaty pens I only have three, but they are fun and rather hard to find.
Teapots I haven’t added one to the collection since 1997, but they range from one from the 1880’s to my mom’s wedding set tea pot ( that she was going to offload for $1 at a garage sale to the buttugly seashell teapot ( my favorite) that was a souvenier from Florida that my mom found for me years ago.
I also am attracted to owls and elephants. Every once in awhile there will be a very nice Owl Collection up for auction on Ebay and it is fun to watch the price zoom up .
Oh, I guess I also collect Maneki Nekos, those Japanese waving cats you often see in Asian restaurants and gift shops, meant to attract good luck and prosperity. I have four, three of which were gifts, but I think having three of anything constitutes a collection. Mine are all white cats since my beloved and much-missed real cat was white, plus they are usually based on the Japanese bobtail cat, which is mostly white with a few intermittent brown spots and a short little tail.
I have pictures of some of my collection stuff here:
I have a fairly extensive collection of various knickknacks featuring characters or scenes from The Nightmare Before Christmas.
I also collect dust and cat hair. That collection is much larger than TNBC.
Coffe mugs. Some humorous, some geographical, some wierd (one has something about “The Straight Dope” on it…).
Swords. Got a couple of those hanging around. Guns, too, though not so much.
The Patrick O’Brien novels. Got all the Aubrey/Maturin books.
Role Playing Games. Even ones I’ve never played, and have no intention of playing.
Die-Cast replica aircraft (small scale, about 1:100 or thereabouts). Got a regular air force on my shelves covering everything from WWI up to today.
I used to keep all of my movie tickets over a span of five years, but I’ve lost interest since I don’t go to the movies that much anymore.
So now I collect the wrappers that teabags come in.
Oh, and pens. Mostly ballpoint pens, but I have quite a few gel and fountain pens as well.
I mostly collect beads. In fact, I think I’m addicted…but don’t wanna seek help. 
I used to collect Wee Forest Folk but don’t really have the money to anymore (prolly cause it’s all spent on beads).
I’m interested as to what the Gun Collectors here actually collect- is it specific themes (ie collectible Winchester Repeating Rifles, USGI issue guns, police guns), or just random guns that take their fancy?
I like “Western” type firearms; single-action revolvers, lever-action rifles, double-barreled shotguns, etc. The rest of my “collection” is pretty much stuff that caught my fancy, but one I built custom-like myself as a deliberate “thumb my nose” at Sarah Brady and the whole “Assault Weapon” nonsense. It almost looks as mean and nasty as it really is.
And FTR: my “collection” is a collection because I don’t buy to resell, unless I know the buyer personally and am very convinced that they won’t do something irresponsible or criminal with it.
My collection is eclectic.
USGI (actual and civilian versions):
[ul][li]1979 Colt AR-15 Sporter[/li][li]Bushmaster AR-15A2 I built myself[/li][li]EA Co. CAR-15 I built myself[/li][li]Armalite (Stirling) AR-180 (older folding stock model – now if only I could find extra magazines!)[/li][li]IBM M-1 Carbine[/li][li]Inland (General Motors) M-1 Carbine[/li][li]Colt 1991-A1[/li][li]Beretta M92-FS[/li][li]S&W Model 10 (for my USN flight gear collection)[/ul][/li]Other military:
[ul][li]1917 Spandau Gew-98 configured as a WWII Kar-98[/li][li]Yugoslavian K-98 with accessories[/li][li]SMLE (I don’t remember what version)[/li][li]Springfield Armory SAR-8 (HK-91/G-3)[/ul][/li]Old West:
[ul][li]1980-something Winchester 94 carbine[/li][li]1932 Winchester 94 (octagon barrel)[/li][li]1967 Canadian Centennial Commemmorative Winchester 94 carbine (new-in-box, uncycled, octagon barrel)[/li][li]Ruger .45LC Blackhawk (7.5" barrel, like Colt SAA)[/li][li]Ruger Single-Six (three-pin, like a miniature Colt SAA)[/li][li]Shiloh Sharps No. 3 Sporting Rifle, .45-70[/ul][/li]Blackpowder (I may forget a couple)
[ul][li]Uberti Colt 1851 Navy (three or four)[/li][li]Uberti Colt 1849 Pocket Pistol[/li][li]Uberti Colt 1862 Police Pistol[/li][li]Uberti Colt Walker[/li][li]Colt 2nd Generation 1851 Navy[/li][li]Colt 3rd Generation ‘Signature’ 1851 Navy[/li][li]Colt 3rd Generation ‘Signature’ Pocket Pistol[/li][li]Ethan Arms Pepperbox[/ul][/li]Other
[ul][li]Ruger 10-22 (stainless, 22" barrel)[/li][li]Sears (Marlin) single-shot .22 rifle[/li][li]Savage semi-auto .22 rifle[/li][li]Ruger Mk.II pistol (4" barrel)[/li][li]Walther PPK (stainless)[/li][li]Walther P22 pistol (green)[/li][li]Ruger Mini-14 (currently with a near-exact copy of the factory folding stock – a pre-ban version that was installed before the now-discontinued ban)[/ul][/li]I think that’s it. I can’t check since they are under lock and key, in a double-locked room, behind an electronic lock. Anyway, the collection is not really specific.
Oh – Another one:
[ul]1897 Winchester Model 1892 rifle (.32-20, 24" octagon barrel)[/ul]
Which radio? The PRC-90 or something older?