I remember spending hours and hours on FreeArcade.com, playing a lot of Java Applet games. I seem to remember my favorites being "Wiz3" and "Tailgunner", but there tons on there.
Once I was fourteen or so, I discovered Newgrounds and (along with SomethingAwful) that ended up being where I spent most of my time online. Even though a lot of the games were kind of crap, I still thought it was cool that people made these games. Not big, heartless corporations, but just regular people who thought it would be cool to make a game.
Newgrounds is still around, and there's no reason I couldn't go on there, I guess I've grown old and curmudgeonly enough to not even think about it anymore.
Maybe I should change that.
Never played FreeArcade, but me and quite a few of my University friends used to go the the Uni Library with every intention of doing a full days work and end up spending half the time on mousebreaker. Those were the days!