Los Angeles

I'm flying to Santa Ana next weekend with some friends for no real reason. I might catch the Blindside/mewithoutYou/The Kick show in Pomona, but besides that, have nothing planned yet. I think the group is going for a more unstructured schedule than we had in Seattle, where we saw all the major sights in a 24-hour period. So, rather than see everything, what is the one thing in the LA/Santa Ana area that I should hit with my fellow travelers?