i lift weights (focusing on upper body, but still including some leg work... hamstrings especially) two or three times a week-- two during race season, three in the winter. last winter i also took a yoga class (loved it! helped a ton with tight shoulders and bad bike posture) and swam a few times a week.
this year i really want to take kickboxing- i've heard it's great for your abs and legs. i'll probably take another yoga class, and i was a swimmer before i was a cyclist, so i'll keep swimming too!
a lot of the guys on my team are string beans who don't want to gain pounds because of lifting weights, but they naturally have a higher muscle to fat ratio than women. the other two girls on the team do lift weights, and a number of the guys do too.
i guess that's not really a hard and fast answer, but in my opinion, just staying in good physical shape will help your cycling, however you look at it