To start with I'm not biased, I used to own a 360 & only sold it to buy a Wii plus a stand alone HD player. As much as I love the Wii if you want serious games (GTA IV, etc) then you've gotta go for the 360 or PS3. I decided to go for the PS3 this time due to the fact that the 360 is so prone to breaking with problems such as the ring of death.
The PS3 feels better built, runs a lot quieter than the 360 & doesn't have that brick of a power block! For looks the PS3 wins hands down in my opinion.
The fact that it's a Blu-ray player as well is a massive bonus especially now that the HD format war has been decided in favour of Blu-ray. It's as good as my stand alone HD DVD player for picture & sound.
Gaming is superb, I have Ratchet & Clank, GT5 Prologue, Burnout Paradise, GTA IV, Call of Duty 4, Singstar, PES 2008 & Drake's: unchartered which are all superb games. Yeah we all know about 360's superior back catalogue but are you really going to play all of them????! For me the graphics on the PS3 are crisper than the 360.
Online is free which is a bonus & I think future compatability has been thought of much more with regards to the PS3 over the 360. The only thing I do miss about the 360 was online gaming with friends as I had approx 30 mates who owned 360's whereas due to its later release, only 4 of my mates own a PS3 but more are on the way!
I also own a PSP, again this means the PS3 comes in to its own. The compatability of remote play between the 2 consoles means you can watch film or listen to music stored on your PS3 anywhere in the world direct to your PSP!
All in all if you're going for a next gen console then this is the one to go for. I loved my 360 but the PS3 is already better & will improve even more once programmers get to know the superior proccessing power of the console better. This price on Play.com (£229.99 at time of review) is an absolute bargain & wont be beaten elsewhere, buy it!!!