Ok I know this may sound crazy because I mostly believe in doing the exercise that you are training for in order to do that exercise.
Have you heard of kettlebells?
http://www.gofit.net/site/gofit/section/83
You can buy them at Target. Anyway, one book I was reading was talking about athletes training with kettlebells (no running) versus those who ran as part of their training. When compared side by side at the end of a training period. those who trained using kettlebells actually did better than those who trained by running. They are a great indoor activity.
As for outdoors, I'd recommend getting yourself some yaktrax if you don't have them already. You can buy them at most sporting good stores.