As of tomorrow, 05/27/16, the only campground open for the season on Tioga Rd will be Tamarack Flat. However, it will be re-closing June 10th-20th.
This campground is entirely first-come, first-served, requires you to treat all water, and is 3 miles in on a rough dirt road (be sure you have a vehicle that can make it). But it does give backpackers with trailheads along Tioga Rd an alternative to the Valley. Get there early if you hope to find a site, especially over Memorial Day weekend.
White Wolf, Yosemite Creek, Porcupine Flat, and Tuolumne Meadows remain closed.
Crane Flat will open on a limited basis, with limited amenities, 05/27- 05/30 only. If you're looking for a walk-in, don't even bother. It's going to be the primary campground handling any and all overflow from the Valley, and sites will go insanely fast.