Okay so maybe I'm late to the party, but whatever, I'm here now! This is a fantastic site, and sounds like it's going to be growing more fantastic-er in the very near future. They've got 600 campgrounds (with all sites photographed) and will add another 100+ this year (mostly in Northwest, but other states too).
You search for sites by state or region, and then once at the park's page, you can look at every single campsite (as well as get some general information about the campground.
This is Cultus Lake, in the Cascade Lake Highway area in Oregon:
Check it out (unless you already know about it and are rolling your eyes thinking "What kind of Airstream travel bloggers are you guys that you've never heard of this site before? Slackers.")