I used to like running. I ran quite a bit in high school, mostly cross-training for swimming, but one season of track also. Every time I've tried to pick it up since, it's just hurt way too much. Probably some of it is psychosomatic, but I think I have problems with the high-impact nature of the activity.

For me, skating beats running hands down. It's much lower-impact and more efficient than running, and on downhills you can carve out turns either ski- or snowboard-style. (Going up hills kinda sucks, though.) Biking is also great, but I don't have good luck keeping my bikes out of the hands of thieves.

suthsc's comment notwithstanding, I really like to "kick it in" during the last ten percent or so of my skate/ride/whatever. I just push as hard as I can (which might not be all that hard if I've been out for a long time) for a substantial distance. It just gives a little extra edge to the joy of exertion.