oh, Tijs. So you're THAT guy. I hate you. =(
I'm late to the party. I finally got around to playing Gears of War 2. Ending was fun as hell, but too bad it it wasn't a challenge.
Between PS2 and PS1 you have lots of great games to choose from, but there's not going to be many (if any) new ones going forward since the PS3 is out now. I'd say if that's not a problem for you, definitely get one since I love mine (despite the earlier models being shit).
On a side a note - I remember years ago when I bought the N64 and the fucking adapter was seperate from the machine, so I had to go out and buy one. Never had to with any of the other Nintendo systems before that. Ridiculous.
I'll second the PS2 recommendation. There are endless possibilities for fun no matter what you like.
Final Fantasy X, Metal Gear Solid(s), Dragonball Z Budokai 3, the Kingdom Hearts series, the Star Wars Battlefront series, Need For Speed Underground 2, the Hot Shots Golf series, Katamari Damachi, the Jak & Daxter series, Dragon Quest VII, God Of War I and II, the Prince of Persia series, Destory All Humans, Dynasty Warriors.
Not to mention Street Fighter, Sonic, and countless other packs and anthologies. The list goes on and on.
I'm a huge fan of the Timesplitters series. They're dumb and lack any real plot but they're SO much fun, especially the multiplayer.
First Person Shooter, developed by the same crew that did Goldeneye and Perfect Dark on N64.