Off the top of my head, I think For Every Closed Door (http://starlingthefool.livejournal.com/tag/for+every+closed+door) is one of the most in-character fics I've ever read. House is very devious and sneaky in this one. It's a crossover with Dead Like Me, but you don't need to know anything about Dead Like Me to follow this fic. It's also one of the best crossovers I've ever read.