Well, there are several ways to go, but my original design with the T1ER was 3 IR sensors used to triangulate the position and distance of a flashing beacon (or remote control). Something you could do is buy a Lego Spybot and modify it, since it has this ability already built in as a GUI program, though it is also open to more advanced modding via NQC.
Some issues do come up with this kind of follower, I.E. it will always be behind you (or the beacon) and therefore cannot pass through doors without additional programming, sensors, and other fiddly bits.
Hope I helped.