Hardware wise, the PS3 is far superior. They even sell PS3s "tied together" in bundles of six or ten to use as supercomputers. It also has much higher reliability; the xBox 360 uses an eco-friendly lead-free solder which degrades over time until components lose their interface with the motherboard and the system has to be returned. (Google "Red Ring of Death")
You can also put any laptop hard drive in a PS3 (and keep your warranty intact; involves popping off a piece of plastic, undoing a screw, pulling a drawer out, swapping the drive, and doing the first steps backwards) whereas the xBox uses expensive proprietary drives. I currently have a 360GB PS3.
You can literally use the PS3 as a media center that plays video, audio, CDs, DVDs, and BluRay.
Read the Wikipedia articles on each. They do have a rather NPOV on both and list each console's hardware components.