The xbox 360 will be the 1st of the 3 systems to come out. The new nintendo is on track to be released in Spring 06, and there are rummors that the PS3 might not be released till winter 06 or 07. The best feature for the new nintendo is that you can download old games onto a memory card. You'll still be able to play games on a dvd, but you'll also be able to download the 1980's versions of Mario or whatever game you miss the most.
The xbox 360 should come out November 2005, but I've heard it might be put off till December 05 so that Microsoft can kill sony in Christmas sales. The 360 can play 90% of the xbox (1) games, no one know for sure which ones it wont be able to run. You can use your old xbox (1) live memory on the 360, and you'll be able to send pictures, musc and videos (online) though live. There will be at least two verisons of the xbox 360, one that has a hard drive (some say it could cost up to $400) and one that does not have a hard drive (around $300).
I don't have a 360 reserved becuase I'm going to wait for a price drop or for a great game to come out. Fable 2, Splinter Cell 4, Baseball 2006, KOTOR 3, or Halo 3, etc. Unless its one hell of a game then I don't go for it. Xbox has more 'great games' IMO. PS2 has the GTA series, but XBOX now has a copy of both Vice City and San Andreas. Xbox also has the Rainbow six series, but I've never been into it. I would have given up gaming along time ago if it wasn't for online play. Its changed the way I game and it feaking awesome to play Halo2, 16 players, capture the flag in the the middle of the night with a controller in one had and a drink in the other.
Heck, you can probably get one of the used PS2/Xbox and an used Gamecube, which runs pretty cheap. But now Zelda: Twilight Princess is delayed until AT least April 2006
Gamecube has plenty of awesome first party titles, and their RE4 is better too. Its a good system, good as primary or secondary, and pretty cheap. PC requires a lot of upgrades and maintence if you want to play games at the top of the line. But they are a good choice if you like FPS or MMORPGs.
Oh, and the Revolution is actually supposed to be a bit cheaper compared to the other systems. Somewhere in the 200-300 price range, while PS3 is looking at 400-500, and Xbox 360 is confirmed at 299 for the base system, and 399 with headset, hard drive, HD component cables, 2 controllers, and some other stuff. (which is a good deal if you bought those seperately.)
Personally, I'm a PS2 fan, but I definitely can see the arguments for any of the systems. X-Box is great for those sports games, and I love changing gears from a long season of a baseball game ot play Mario Party on my roommates Game Cube.