Runescape! I can't seem to quit, and when I was finally getting bored of EOC and in the quitting phase, they release Oldschool which was a checkmate for me.
Pokemon for the first origional game boy.
I never got off that as a kid.. Literally I'd get up, play Pokemon, eat, play Pokemon, drink, play Pokemon, eat again, play Pokemon, go to bed, pla Pokemon in bed, sleep and repeat. I must have gone through like £1,000,000 worth of batteries...
First was Heavy Gear 2. This addiction was broke since this game won't run on 7.
Gearhead garage is another. This addiction broke for the same reasons as above.
Runescape is one I've always been addicted to - But I haven't been able to play this since I've got crappy internet now. It ran ok on dialup, on xp, but refused to work on dialup on 7. Then I switched over to satilite internet and the ping kills me. Before this I was playing on DSL from 06 to 08.
I'm going to (hopefully) switch back to DSL in a week or so, since the lower speeds are avaliable in my area. (1 Mb speed - Half of what my satilite is, but the much lower ping will let me make more use of it) Funnily enough, once I switch back, Runescape is the first game I plan to play.
RS and Counter strike source. They weren't really addictions though, I mainly played because of friends and the community, and got bored after a while so I stopped playing.