I second Crater Lake, and would suggest the coastal CA drive. And if you are going all the way down to Death Valley, I'd suggest seeing Sequoia after Yosemite and then over to Zion and Bryce. I really enjoyed those two.
Gosh, I just realized that there are so many fabulous national parks that a person would need months to see them.
I find it hard to pick my favorites because they all have their unique attraction. But all those are worth the time and effort.