The Slicer by Ice Meister allows kids to sled year round, using ice blocks attached to the bottom of the sled as a propeller during summer months. With its contoured shape and low profile runners the Slicer functions as a normal sled perfect for snow, but the detachable ice packs can provide up to two hours of sled-time in hot weather (they can also be stored under the seat of the sled when not in use). Fill the packs with water and stick them in the freezer, then reattach, find a hill and hang on tight. The durable construction supports up to 200 lbs, making it fun for most thrill-seeking adults, too.
You can buy a Slicer from their website for $70 (includes a sled and two ice packs).