I just want to put a plug in for cycling and swimming. If you work on your technique in swimming, you can join a club, etc., it's truly a fantastic, superhard workout; or alternatively you can get in a groove with your stroke and completely zone out - I think it's because of the ways in which you have to coordinate your breathing. And while I also find cycling indoors a bit tedious, it's totally fantastic outside. If you were willing to run in snow/terrible heat, the same can be true for bicycling. I'd rather keep my own knees as long as possible and enjoy two new sports. After 3 years without running, I'm thinking of upgrading my bike and maybe even buying a triathlon wet suit so I can swim outside into the fall/early in the spring.