Damone, how'd I know you would choose UFC 49 before I even clicked on this thread?
Seriously, though, UFC 49 is probably the most solid, all-round event that I've seen. It features my favourite highlight reel knockout in Thomas/Edwards, a short but awesome scrap with Eilers and Kyle, and my favourite Diaz fight against Parisyan. I could've lived without seeing Lytle/Jhun, but still, it was solid. Like Damone mentioned, there's White/Liddell, which is also my favourite Chuck fight. Very fun scrap.
Couture/Belfort is a whole other story. Couture makes Belfort pay dearly, and sort of toys with him in a very punishing, brutal manner. He puts the hurt on Belfort, makes him bleed like there's no tomorrow, and becomes the champion again. Couture, as always, rules.