Not a fanboy, but I find the PS3 a bit better...
The xbox 360 controller is better to hold and works great for FPS games (Halo etc.), but it gets too sensitive in many other games ESPECIALLY in platformers and some racing games. Also, the xbox 360 controller cannot be recharged unless you pay for a kit with rechargable battery and a propietary cable. The PS3 controller is rechargable and you can use any USB to mini-usb cables to charge the controller.
The PS3 has slightly better graphics, but a lot of unused horsepower. While more expensive to buy it's cheaper in the long run, especially if you enjoy playing online. Also the playstation store has a lot of good offers every week, while XBL only has one offer per week, usually for some sh***y arcade game. Physical games, are, however more expensive as well, but considering the features it has (blu-ray player for one), it gives a bit more bang for the buck.
If you get an xbox 360 and you want to get XBL gold, DO NOT ORDER A GOLD SUBSCIPTION OVER XBOX LIVE USING A CREDIT CARD, You need to cancel the subscription by calling microsoft (in most countries), which can become hard or time-consuming. Instead, get gametime cards, which are usually cheaper.
Upgrading the hard drive (which will be needed if you get an 360 Arcade or a relatively small model) on a 360 is expensive. Xbox 360 harddrives are VERY overpriced compared to the PS3, which can use pretty much any standard 2.5- inch harddrives up to 500 GB (for now)
Media-wise, the xbox 360 can play CDs and DVDs, while the PS3 can play DVDs and blu-ray discs (older models can play SACDs also, which are high-def audio CDs). The Media center in the xbox 360 is also severely limited to basic .avi, .wmv, .mp3 and .wma files, it cannot play DivX and such without a transcoder progrm on the PC.
Network-wise, the PS3 has built-in wifi, while the older (white) xbox 360s require an addon. Also it seems like the PS3 limits its bandwidth usage as downloads take a bit longer. On the upside, though, the PS3 has a fairly capable web browser. It's a bit sluggish, but good for fetching walkthroughs and such while playing games.
Both consoles have loads of peripherals and add-ons, but xbox 360 peripherals seem to be a little pricier, at least here in Denmark, so make sure to browse the net for good offers.
The PS3 also has a lot more options for customization, including giving you the ability to make your own themes. On the 360, you can only change the background.