To throw more fuel on the decision, get a PS3. I have a PS3, my brother in law lived with me this past summer and had a 360, PS3 hands down.
1) PS3 is a bit more on initial cost, but in the long run I think Xbox nickels and dimes you out of everything. The PS3 comes with the wireless and Blu-ray built in, plus it is compatible with run-of-the-mill bluetooth, so your earbud from your cell-phone works with the PS3. Those add ons to a Xbox can add more than 300 hundred dollars to the initial cost. Not to mention you have to buy XBox Live time, but every single bit of online PS3 play is absolutely free.
2) I think the graphics are much, much better on a PS3 than a 360. Like I said, my bro-in-law lived here over the summer and we had my PS3 and his 360 attached to my 1080p Samsung DLP. The PS3 blew the 360 out of the water. We even tested both with straight up red/white/yello AV cables and the PS3 looked much better.
3) I will admit, one downside is the absence of some games from the PS3 lineup. However, for me, that wasn't as big a factor in my decision. I've played the new HALO, and while it's cool, it's not the be-all-end-all to games. Granted, I'm not a super-hard core gamer, so not having some games available doesn't make me lose sleep at night. It might to you, but the current line-up of games keeps me more than happy.
4) I like the built in rechargeable batteries in the PS3 controllers. It's a small thing, and I know you can buy rechargeable battery packs for the 360 controllers, but, guess what, another nickel and dime of the 360.
5) Blu-ray, in my opinion, is winning the hi-def video battle right now. Don't believe me? Go to Wal-Mart/Target/the Nex/etc, and see how big the Blu-ray display is compared to the HD-DVD one, and then notice how many empty or less than full Blu-ray spots there are as compared to the HD-DVD. Not many appear to be sold. In addition, Blockbuster dropped HD-DVD, and more movie rental stores are starting to push Blu-ray than HD-DVD, which will help Blu-ray gain the foothold.
6) Sony is in the process of developing their systems/software to allow owners to install third-party operating systems on the hard drives. In essence, they would be creating an all inclusive computer and game system. The article I read is their goal is to make the PS3 not only a gaming system, but a family entertainment system as well. Plus, Sony seems to be constantly updating the system with game updates and system updates.
7) I don't remember about the 360, but the internet access on the PS3 is a nice feature too. When I get done rocking out on Guitar Hero, I can then surf on over to Airwarriors to get my fix
8) I can't attest to the processor performance the Statesman has referred to, but I've yet to have any kind of issues with any of the games I've played.
It does come down to personal preference, some people just don't like Sony or just don't like Microsoft. That said, I think the PS3 is the better choice cost wise as well as performance wise.
Oh, and if anyone is interested, my s/n on the PS3 is insanebikerboy too.