Join an exercise class. One guy's experience:
About a year ago I started regular pilates exercises which seek to develop controlled movement from a strong core, emphasizing deep abdominals, the pelvic floor and inner and outer thighs—all the muscle groups used during sex.
In a short time I noticed a marked improvement in my libido and the firmness and endurance of my erections.
The gym I go to regularly offers free classes several times a week and I have a couple of videos I use at home—I started with "Pilates Workout for Dummies."
The other great thing about Pilates is that most of the others in the class are women, who I'm sure are there for the same reason I am—to take care of our "love muscles." Fortunately I am happily married to my own karezza-lovin' woman, but I have often thought if I were single...
So I don't know if the greatest benefit is from strengthening the muscles or being in a closed room with all that estrogen and the soft Asian melodies. Whatever, I'm a believer.