I think this fits me perfectly.
Used to collect comics and trading cards as a kid - mostly I collect cigarette butts and bottle caps. /sigh

Games, hardware, PCs (I'd like to get every single piece of x86 metal Intel made so far; like, an 8088, an 80286, an 80386, an 80486, a Pentium and so on)....

I pretty much just collect games.
I also collect books. I've got way to many of those. It doesn't help that there's two giant used book stores in town.
When I was younger I had a collection of transformers. I have them boxed away, because I don't really collect them anymore :\

i collect v-cards

*whistles*
I'm trying to get rid of mine, but overtime more people got involved in my transformers collection (family members, friends...). They like it as much (if not more) than I do. My birthday is in 2 days and I bet you that I'll probably get a couple Transformers. Haha.
So instead, I got rid of other collections that I had. :D

I collect games...and some graphic novels.
I have maybe 160 games in total. I have 74 games on Steam (16 are Everquest games and expansions.), 5 on GamersGate and from the Humble Indie Bundle Pack, 7 on Direct2Drive, 9 Nintendo DS games, 35 on GOG if you count expansion packs, 2 of Charlie's games, Sleep is Death, and 21 on Disc. And those are just commercial games. =)

Well that's still a step up from Alias's dust.

i collect guitar plectrums, but since the little buggers have a tendency to disappear into thin air, my collection is steady at 3 plectrums(it did peak at 5 some years ago)!

I used to collect US currency for fun, but recently had to sell them for half their worth due to being jobless. I still have a 2 dollar bill.

Guitars. The sad thing is that I hardly play these days, but I still buy the occasional one. I like to try and buy ones that I either really want or just ones that I need for a particular purpose, but often it's just because. I also try to always get something that has a unique feature. For example, my last one was a Randy Rhoads 24 fret guitar (that model is usually 22). Previous to that was an 8-string and one of my collection has 27 frets. Sometimes I get one because it has a particularly pretty finish or it's a brand I've never owned before. Crazy in a way.

I collect games, consoles and apparently I collect mugs (as I seem to have a s***load).

If you have many G1 you might make enough $ to put a deposit down on a house by selling them.

I keep anything. My room is filled with cardboard boxes for PSPs, iPods, and two PS3 boxes. And more stuff.
I also collect dead bodies but that's something I am not allowed to talk about in the presense of my parole officer.

Currency...... I've got some from 74 different places I have been to so far. US Currenecy however I go for the more rare stuff.
Games are another, lost count....
OHH Passport Stamps... :) Im on my 4th new passoprt in less then 10 years :)

I used to be an avid stamp collector back then...