The graphics are similar, some would say that xbox 360 has better graphics while others will say that ps3 does.
That is indeed debatable. I personally can say it's undisputed that the PS3 has much better hardware, and has the definitive graphics superiority on exclusives, but not multiplatform games (Take account - Something like Madden 08, the 360 version ran at 60 fps while the PS3 version ran at 30fps)
Here's my comparisons -
Graphics - PS3 wins in exclusives (Devs put more work into it, and have just about unlimited limitations).
Online - 360 wins in online, but you have to pay about $50 every year to play with others (I believe you also have to buy a wifi adapter?). The PS3 comes with an adapter installed, and the online play is free.
Games - 50/50. The 360 DOMINATED 07 with games (Halo 3, Bioshock, etc), but very little is planned for 08 (Atm all I can think of is Gears of War 2). The PS3 did fair in 07, but the new, big releases are coming this year. Those include things like MGS4, LittleBigPlanet, etc.
Hardware - Another PS3 win. The 360 is ravaged by the Red Ring of Death, and although this is being fixed in newer models and you get a warranty, it is still a big thing to consider.
Overall, I'd really have to say PS3. It's cheaper (technically, if you include XBL) and the big games are coming out this year.