Along with everyone else here, I love Rent. I've unfortunately never seen a production of it, but I've seen the movie several times and own the DVD of the final Broadway performance (Haven't watched it, though).
For shows I've actually seen productions of, my favorites are:
Hamlet
The only time I've seen this show was at the Oregon Shakespeare Festival in Ashland, Oregon last April, but god damn, that was amazing. The lead was fantastic, as well as the touch of humor that was added to the show. It fit very well, and made it massively entertaining.
Cat on a Hot Tin Roof
Again, this was at the OSF. The structure of the show is very interesting, as the first two acts are essentially monologues, by Maggie and Brick, respectively; with only the third act having more than two or so characters onstage at once. But it was emotional, daring, and despite the fact that it was mostly just two people talking, very interesting.
Dead Man Walking
Last year, my high school was picked to do a production of Dead Man Walking, Sister Helen Prejean's story about a death row inmate and her attempts to comfort him on his way to the deathbed. Although it was performed entirely by high school students, it was damn good. The lighting, acting, set, and pace were all fantastic, and I'm not just saying that because I was part of the tech crew. It was an amazing show.
