I have an affinity for small robots based on insects. This Scarab robot kit by Elenco features two touch sensors which detect obstacles in its path. Once it detects an obstacle, the beetle will execute a two-step maneuver to bypass it. The robot is capable of moving left, right, and in reverse. This kit is rated at an intermediate skill level, so if you want to hone your soldering skills this is a fun and affordable way to do it.
Here's a link to Elenco Scarab Robot Kit (soldering required).