Pretentious does not = bad.
Most art-rock/art-core will be pretentious as hell, but often times it ends up being really good, in that aquired taste kinda way (Blood Brothers being my own, personal example).
Jam Bands like phish and the dead are the type of pretentious I just cant get into.
Prog-Rock has to be pretentious. I think thats one of the rules. But boy, I love me some Genesis, Mars Volta, and Sunny Day Real Estate/Fire Theft
Just about all "emo" is pretentious. I mean really, who gives a fuck about your feelings? (Millions of teenagers (and me) all across america!)
Costumes - Wearing costumes makes you both pretentious and ridiculous. I'M LOOKING RIGHT AT YOU, THE LOCUST/AQUABATS!
Oh, my
I would say The Mars Volta is my favorite pretentious band.