It's been a couple of years, but I dusted off my Rollerblades last week and have since taken them for a couple of skates around the city. Okay, maybe it isn't the "cool" thing to do anymore, but it's low impact (unless you fall) and still a heck of a lot of fun! As an added bonus it's a great core workout. It forces you to work a lot of those muscle you forgot existed and I'm told it great for developing a sculpted backside.
My lower legs have been in a world of hurt from running too far last weekend (stupid soleus), and I needed a low impact alternative. Blading was the ticket. I can still get a high intensity cardio workout without destroying my legs. For anyone experiencing shin splits or knee pain from too much running I highly recommend it. For the rest of the summer I will be alternating between running and blading.