For summer, i personally recommend these two activities:
1) Mountain biking - super fun, adrenaline pumping, GREAT exercise, great for keeping those snowboarding legs in good shape for the winter. Quite expensive though, since a good MTB will cost you at the cheapest $600.
2) Longboarding - ridiculously fun, especially when cruising park paths. Great exercise for one leg, so be sure to practice switch to change things up a bit. Scary when going downhill, considering a speed check consists of sliding four pretty grippy wheels. Expect some road rash. Chicks dig longboarders, at least in my area. Great transportation method too. A good longboard (Landyachtz-level quality) will be ~$250 at the cheapest.
Make sure you protect your noggin' with a good helmet for both. Pavement is not as forgiving as snow.