I've been running off-road for years. Over the last year though I've been running in something called the "Vibram Five Fingers Sock". Effectively you are running barefoot with just a small amount of rubber to protect your feet; you've got to run in a different style to the running shoes we've been used to with impact protection in the heel (try reading Chi Running for an explanation of how to run differently, whether Tai Chi is your thing or not the techniques in there do help). And if you want any inspiration about what you might do next I suggest you buy a copy of Born to Run and the Barefoot runner's handbook....