This chassis is cute, red and has two DC motors so its super easy to drive from the Crickit's dual DC motor port. You may need to use some wires to extend the DC motor connections (they're a tad short)
Mini Round Robot Chassis Kit - 2WD with DC Motors
This chassis is nearly identical, but has 3 layers, so you can FIT MORE STUFF!
Mini 3-Layer Round Robot Chassis Kit - 2WD with DC Motors
This chassis is not as nice as the above, but if you fancy it, it comes with two servo-style DC motors and can use the DC motor control on the Crickit as well