I went to Osh, Bishkek (two main cities, Bishkek was more fun), Lake Issyk-Kul where I didn't see much because I was sick, and I did a 3-day horse trek to Song-Kul lake which is highly recommended if you can ride. I slept in Yurts, ate with local shepherds and trekked through a valley and over a mountain pass to get to the lake. Great fun.
It was about 4 years ago now though so I can't remember many specifics.