There are different kinds of Moogs, of course: there's the Minimoog line, which are self-contained synths like those most people are familiar with; and there are the full-size System 55 and such, which are the modular ones.

Afaiu there are a whole bunch of X-Y touchpads like Kaoss Pad, both as separate controllers and integrated with others, like in nanoPAD2. And there are also apps for phones and tablets, like Bebot. These aren't particularly related to modular synths, but likely can be used with them for input.