The NFL Sunday Ticket app, actually. We can't have a dish where we live, and since moving away from FL had been watching the Bucs games mostly at Buffalo Wild Wings, which was inconvenient, noisy, and expensive. There is a ton of complaining on the official PS3 boards about the quality of the feeds, but we haven't had many issues.
Anyways, since I already had a 360 and Wii, I didn't think at first I'd be using it much for gaming, but now it gets as much time as my 360 and way more than the Wii. I'm glad I went with the 320 gb since I'm buying tons of stuff off PSN now.
ETA: Actually, the original choice between the 360 and PS3 I made in '09 was very close, could have gone either way. I was a big PS2 fan.