Rock Creek Resort is just below one of the most beautiful places in all the Sierra...Little Lakes Valley. LLV is a great place to start for a flatlander
Ditto that. LLV was the first Sierra hike I took my wife and daughter on when they came with me last year, and it was perfect for them for a first day's effort at 10K'. Gorgeous setting and only about a 600-foot gain over an easy 7-mile out-and-back. Gets you accustomed to the thin air without a strenuous, headache-inducing effort on that first day.
As Steve suggested, a good Day 2 would be the Methuselah Walk through the Ancient Bristlecone Pine Forest on White Mountain (CA 168 near Big Pine). Again, you begin at about 10K', but there's more cumulative gain over this 4-mile trail, and it's never very steep or strenuous. These are two good acclimation hikes for those of us from the east.
You have plenty of higher-altitude, greater-gain options after that along the Eastern Sierra, but Telescope Peak in Death Valley (11K') is a good change of pace, and the views are magnificent (one of the few places in the lower 48 that you can stand and look almost directly down for more than two miles). Also, the trail to the summit of White Mountain is the easiest Fourteener in California. If you're planning to wind it up with Whitney, however, be careful that you don't overdo it - you want your legs strong and fresh for that final 6200-foot gain!
