Solarbotics has just released a couple products that are "A" word compatible, and you know what that means, they are EZ-B friendly as well! Those new products are The Brutusbot
And the EZ-B Faceplate for the Solarbotics Arduino/Freeduino Enclosure (SAFE)
So if you are unsure of what to hack your EZ-B into, you could always start with a SAFE and add some servos and wheels to it, or you could mount a plush toy onto the Brutusbot Chassis as a base for your next mobile EZ-bot (just add an dual H-bridge motor driver).
I'm sorry if this sounds like an ad, I really am that excited to see more EZ-B compatible products out there so everyone has more choices in what to hack and to make easier to do so.
Here's a video of the Brutusbot Chassis in action (and yes, I am the long haired madman in the video):