two-way communication?

Howdy folks!

Been away from the robot community for a while, and in getting back to it
I'm digging up some bots I was working on a few years ago, but never
finished.

Back then, I was 68HC11 primarily, and now want to switch over to PIC-
based.  Question is, I need these two to communicate now and then (not very
often, and just a few bytes here and there).  What are folks doing these
days without going to high-end radio, bluetooth, or Wi-Fi for communicating
between multiple bots?

These guys are little (palm sized) and may be out of sight from each other,
so line of sight isn't guaranteed (otherwise I'd probably try infrared),
but the distance will be under 25ft.

TIA
Steve