Also great for the toddler/preschooler:
the Mini Micro scooter . It's a three-wheel scooter, but the two wheels are in the front. The front bar doesn't turn (no need to steer), instead kids turn by leaning their weight on either side. Much easier than the other 3-wheelers. My little guy has been using this since 18 mo, whereas he is just starting now (2 years later) to be able to ride on the razor. Expensive, but highly recommended!