If you are in CA, then Crystal Springs is a good bet. Lowell Invitational in Golden Gate Park is run on a pretty nice course as well.
I'm pretty sure that there are a couple of meets run on the beach, hosted by some NCS teams. I want to say Clam Beach up by Arcata is one. That's a heck of a drive though unless you are already close.
I've never been to any of the meets in SoCal other than Mt. SAC, so I don't have a lot of input. You could try that course they ran as a state qualifier in McFarland, that looked pretty scenic ;).....Stallion Oak Regional? WTH?
You could always come to Hughson for our epic mud pit.
http://www.hughsonsupercross.blogspot.com/
We do have a lot of loops, but they are interesting loops, at least. And everybody gets a popsicle.