I've been doing squats and other lower-body exercises to work on improving my cycling legs, mostly focusing on strength; however, now I've started incorporating power training using explosive moves with lower weights and I can really feel the difference on the bike.
I've been using the Ground Based Jammer in the gym. I get in a low-squatting position (for this I stand on an 8-inch platform, so I can get in below "parallel" squat position) and then I propel upward with near 100% force. I do this with both legs and single leg exercises.
Video showing the Ground Based Jammer