I used to collect Matchbox cars. I still have the collection without any additions lately. I now collect music.
Legos. Lots of legos, lemme go have a look around.
9 random shoeboxes between 3 floors
The following ziplock bags:
Most of a Space Shuttle/launchpad
Several sci-fi submarines
Most of a large blue/white/clear orange starship
A Trojan Horse built for extra-credit in Latin
Some basic bricks
A hospital
2 medium-sized pirate ships
2 Mercury-ish rockets
All sorts of random Technic stuff that I regret buying
Thomas the Tank Engine, and track/transformer to run him on
Whats left of the ancient Egyptian set I recently used for Thomas
A pizza place
Several mostly assembled castles, along with a Viking ship
A big box of small cars, planes, and helicopters
Surely I’ve left something out
Also Final Fantasy soundtracks
I collect cheap plastic snowdomes from places I travel to. Some of them I need to replace because for some reason the water eventually starts to evaporate.
Antique bookmarks, I only have a few, but I like them very much.
I used to collect shoeboxes.
I always thought they’d come in handy one day… When I put my stuff in storage for a year, I had to throw them out.
To stop the addiction re-occuring, I don’t buy shoes anymore (being poor helps) or if I do, I make sure I put the box in the outside bin that day. If I leave it inside overnight, I know it’ll never leave the house 
Gosh, where to begin? Like many people with an irrational fear of being alone, I compensate by surrounding myself with collections of things to bring comfort and order to my tattered existence. To wit:
153 old Mad Magazines.
A few old still cameras, from the 1920’s-1940’s.
Old fountain pens. I used to collect them with great zeal, and only buy really cheap abandoned ones at flea markets and junk sales and then buy replacement bladders and write letters to friends with them. Then I got a computer. 
Embroidered patches, but only from jobs or situations I’ve been in. Film industry and EMT-related stuff.
Fat Cells. :rolleyes:
Cartooniverse
Studio gear - Old keyboards/drum machines, etc.
I also have a small collection of computers, but I’m running out of room so I need to get rid of them. Well,. most of them. I’m keeping the ones I have the boxes for (Vic20, C-64, TI-99, and a couple others). But do you know what a pain it is to move an IBM system/34? The thing is like a million pounds.
Music boxes, about 30 or so at last count.
Sugar wrappers (and the wrappers from salt, pepper, or cream–I’m not choosy): nearly 1600 last time I checked.
Oh, wow…
Like Cartooniverse, I certainly have collected more than my share of fat cells… actually, I’m happy to know I haven’t completely cornered the market
But as for things I’ve actually wanted to collect:
Matchbooks from places I’ve been, although those are almost impossible to find today, and
Coffee mugs and/or beer steins from places I’ve visited. When the pictures are put away and the bills are paid, looking at them on the fireplace mantel brings back fond memories…
Oh, due to the above, back to things I seem to collect whether I want them or not, dust bunnies 
Mike
Cool-looking tags (like from clothes).
A few years ago my mommy gave me a tag from her jeans that was one of those tags you’re meant to keep (that have keychains on them) and then when I moved into my new room I started hanging them around my window (for decoration)… now I have 80+, I’ve had to move to the door frame.
When I was little I used to collect those little puffball things with the feet you stick onto your desk.
Oh yeah and upon preview, Merhouse reminds me that I collect matchboxes (especially if they have pretty matches with colorful heads (like the pink ones I got in St. Martin)).
Swarovski Crystal
Royal Doulton Lady figurines
Nothing else matters
Ah, collections! Well, I collect certain special coins… I presently have more than $55 in coins and bills of varying denominations. They have to be pre-1970, though… unless they’re foreign or miscellany! For example, I have an Australian halfpenny from 1950, and an Australian 20-cent coin from 1969. I even have Canadian nickels from 1940 and 1957.
As for what else I collect: I have nine Bathroom Readers, all of the “Outlander” series by Diana Gabaldon, plus lots of other books on various topics. Don’t worry, because I too have spent a lot on books! (especially within the last couple of weeks)
Also, I have stickers, a fair number of CDs, and a lot of info on people! Saves time remembering when peoples’ birthdays and stuff are when you have it on a huge database on the computer, LOL.
I definitely collect friends! Handy to have around, as you don’t know when you’ll need 'em! (used to collect a lot of them on ICQ, but recently deleted almost half of my list since I don’t talk to them anymore… last time I added someone was in mid-January)
Inadvertently, I collect a lot of dust, as well. Probably a lot of semingly useless stuff, too.
Flexible Flyer sleds. I’ve had mine since I was five (1959) and my folks were so swell that they took it with us in our move from Connecticut to southern California. I took it with me when I got married and moved to Oregon in 1973. It’s the fastest thing on the hills – my true adventure-friend.
A few years ago, I busted a side rail (fancy that – a sled built for a five-year-old supporting a wild, now-overweight, adult for twenty-plus years, then busting! Grr.) So I started viewing sleds on eBay.
Have a mess of them now. Most were overpriced but there’s just something about an auction… (I’m better now.)
Stopped about a year ago, for good. I’m satisfied, and repairing my original.
Well, frogs. Both my husband and I like frogs, so we have them all over our house. Frog candlesticks, frog bookends, etc. Our collection got unwieldy so we’ve been much more selective lately.
I also used to collect vintage children’s books written by Mrs. L.T. Meade.
Now, I collect antique oil cans. Not the branded ones like pennzoil, but the ones with long necks in copper and brass and other metal. It gives me something to look for when we’re in antique shops (we go in them to look for antique tools for the husband).
Huh? What? 
[inner thoughts]What’s this? Is this that “flirting” thing that everyone talks about? Or is he talking about someone else? Should I check his past posts to see if his SO is named Kat? Will I look stupid or just clueless if I make a comment? [/inner thoughts]
wanders about aimlessly, bumping into furniture
I collect small empty boxes. If it looks cool, I’ll stick it on a shelf somewhere. I’ve got a little box made from bannana leaves, some with oriental designs, a leather box that some cologne came in. All sorts of odd looking boxes.
In hindsight, I’m a big dork. Kind of like Steve Buscemi in Ghostworld, only less cool. 
I have a small but expensive collection of Major League Baseball authentic jerseys and T-shirts.
Blades. Swords and Daggers, mostly, plus some antique hunting knives that belonged to my grandfather. I have a not-too-shabby collection, hasn’t really grown much lately, but in the future I plan to have “one of each.” I avoid the stupid “sure to be a collector’s item!” blades and concentrate on reproductions of actual historical pieces and/or styles.
I guess you could call my Nigel Tranter novels a collection - I’m trying to get my hands on everything he’s written. But that’s just because I like the novels and I’m interested in the subject - Scottish history.
Wind-up toys. The cheap plastic variety which can be found at garage sales.
Also bootleg concert tapes, mostly Grateful Dead.
Playing cards. I don’t know how I started, but I’ve now got over 300 decks of varying provenance. Among my favourites: a deck from c.1870 from New York State; a 1915 deck from the Fred Harvey hotel chain, which shows pictures of “the old West”; a 1950’s Mexican deck which depicts bulls and famous matadors; and at least one deck from every casino on the Vegas Strip. I also have cards from at least 25 countries, from Iceland to Libya (!). It’s a surprisingly inexpensive hobby too…the most I’ve ever spent on cards was $25 for a mint-condition C&O Railroad double-pack.