For trilogy's I'd struggle to name any...sequels are much easier, my top two being Terminator 1 and 2 and Alien / Aliens.
LOTR was OK but I've only ever seen them once and it's not something I'd rush to see again.
Trouble is so many films are hyped to death and then there's the whole 'Emperor's New Clothes' thing with director's...everybody raves about this director so he must be cool, his films must be good and I must like him...Quentin Tarrantino springs to mind