iRobot Create vs. Roomba Red
The iRobot Create robot is very similar structurally to a Roomba. It uses the same framework as a Roomba but omits the vacuum parts (to give you more battery power for your own projects). It also improves on the Roomba from a robotics perspective, by having a swivel front caster and an optional back caster.
Of course, almost all Roomba accessories work with the iRobot Create. For instance, here I've plugged in a normal Roomba battery instead of the green AA battery holder the Create ships with.