In Mini E I'm using the Pololu 75:1 gear motors with Lego wheels that are attached to the shaft with these that Duff makes.

I think that other people ether make there own wheels with this sought of hubs built in, or they use something like these

Ohhh, and in terms of motors, I think that a lot of people use the 50:1 Pololu motors for more speed.

Hope this helps