What are some good exercises to complement swimming?

[cemaphonic]

After years of not nearly enough regular exercise (I am reasonably active what with chasing around a two-year-old all day), I'm trying to get into the swing of a regular routine again.

I've always liked swimming, and we have a city pool a few blocks away, so I've started doing that for about 40-60 minutes, 3 times a week. What are some good exercises to do on the alternate days. Preferably, exercise I can do at home, since the most convenient time for it is when my boy is napping.