I'll be using Erector's "Spykee Wifi Spy Robot" as the basis for the project. It's marketed as a toy but I've owned it as well as Rovio, and for the money, Spykee is remarkably robust. It has a much longer battery life (2 hours versus 15 minutes) it has far, far lower latency during control (Rovio is cool to look at but nearly uncontrollable over the net) and better for outdoor use (sturdier, has tank treads, more powerful motors). The portion of Spykee that has all of the electronics in it is pictured below: Not pictured; the "head", essentially a webcam with integrated LED flashlight. The rest is the non-functional upper body and arms which I won't bother to assemble as they add nothing and make the robot easier to tip over.
Unlike Rovio, Spykee doesn't rely on being indoors for the navigation system to work. Rovio uses the "Northstar" system, which tracks it's position by IR lasers pointed at the cieling. If it isn't obvious, while I love Rovio's aesthetics and added functionality (the movable head mainly) it's the wrong robot for the job, and a somewhat shoddily built one in general. All things considered, if we're to have multiple robots they need to be affordable and capable. Spykee fits the bill on all accounts. At least, a stripped down "base plus camera" version of him.
I'd also like to add some form of manipulator to each robot. Has to be passive as the system doesn't really permit the integration of complex robot arms or anything like that. Think bulldozer shovels, prods, picks, that sort of thing. Suggestions welcome. Oh, and you may want to download the Spykee control software in preparation. He's currently controllable via your iphone/ipod touch, your PC, your Mac, and your Android phone.