Are you going through Southern Utah at all? Lots of cools stuff through there, but it would be a bit out of the way.
I'm guessing you're going through Needles on eastward? Hmmm..... I'll have to think about cool stuff along that route, it's been 2 or 3 years since I've gone that way.
If you are taking 10 all the way to LA, grab 15 and hit vegas, definitely.
Pheonix is a cool little stop if you want!!!
If you are splitting on 8 towards San Diego, that whole mountain trip is fun. Definitely check out downtown SanD, including the gaslamp district. I'd PERSONALLY skip TJ (just south about 10 miles).. at least after the first time I have seen it. it loses its interest after that.