Moby. Probably my best overall to date.

Started with good old rover base. 

Mega and motor controller

Then switched to omniwheels.  Can move in any direction, rotating all the while, if you like. 

Sonar on a servo. 

And bluetooth.  Really nice autonomous open path seeker. Can be commanded via bluetooth as well. 

Tweak hexapod

Just a fun storebought kit.

IR follower.