Take the High Sierra Trail from Crescent Meadow out to Hamilton Lakes and back. I think that is about 33 miles round trip, and the last mile or two to Hamilton Lakes will kick your butt.
Or, the Mineral King route that I did a few weeks ago was about 37 miles. That took me three days. Timber Gap, Hamilton Lakes and Kaweah Gap, Big Arroyo, Lost Canyon, Sawtooth Pass. I had thought about Black Rock Pass, but it looked awful.