Supercross BMX Balance Bike - they look terrific. Actually, the DK Nano, Strider, all kinds of them are really good. Just look for decent bearings, actual pneumatic tires, spoked wheels, etc. Then show up at your local track to 'race' (or at least watch!). There is little as adorable as the balance bike classes at BMX races - there's a free one-day membership to try, and if you want to keep going it's $30 a year, and balance bike races are free. (when you start full track pedal bikes, it's $60 and $10 - your prices might be slightly different)