my fave is the mondrian--the location can't be beat (right in the middle of sunset strip), the rooms are cool and minimalist/all-white, and it's got a cool vibe to it. the restaurant, asia de cuba, has fantastic food. and you can walk to a lot of things.
lilykind's rec is great, also.
there's also the standard, right down the street from the mondrian, which is cheaper and louder--great pool scene and fun lobby bar at night.
I talked to a friend who's well tapped into the LA party scene and he highly recommended the Standard (the budget option) and the Mondrian (thought warned that the Mondrian doesn't come cheap) as well as Chateau Marmont.
He also likes the Sunset Tower Hotel (aka The Argyle) and adores the hotels run by the KOR hotel group (I think he wants to move into the Viceroy in Santa Monica because of the decor...hehe). The KOR group operates the Chamberlain in West Hollywood....though that seems a bit quieter than what you're looking for.