"War doesn't determine who's right, war determines who's left." - Godfrey (Fallout 3)
"It's the strangest thing. Yesterday, it was hard, today, it is easy. Just a good night's sleep, and yesterday's mysteries are today's masteries." Level-up message from Oblivion
I know neither are incredibly funny, I still like both of em, and now for some more humorous ones.
"I may be drunk, Krogan, but you're ugly. And tomorrow I'll be sober." - General Septimus (Mass Effect)
"Anyone who fights us is either stupid or on Saren's payroll. Killing the latter is business. Killing the former is a favor to the universe." - Urdnott Wrex (Mass Effect)