Check out this Slideshow from last year's Bonnaroo composed of a few of my favorite photos and acts. I had a really amazing time, and tickets are quickly running out for this year.
Also, if you are heading to SXSW check out Last.fm's handy Band Aid Group/Application. I noticed a few good recomendations with my account including Bon Iver, Zykos, Asobi Seksu, and a handful of others. Definitely worth a look if you are headed there or just looking for a few good recommendations.