More than just your typical ooga booga caveman communication skill set.
Indiecade -- the showcase of independent games that has yearly space at E3 surrounded by a white picket fence -- is always a mixed bag, and rightly so. I support experimentation, and it's not always going to work. That being said, it's always nice to get hands on time with a game in that area that doesn't rely on physical gimmicks or political statements, and just gives you a creative idea or good old fashioned solid game design.
Tribal & Error was this year's discovery for me. Described as "a game about language without language," this point-and-click puzzler by Grotman Games revolves around learning to "speak" caveman through context by recording and playing back the caveman grunts in different combinations to form new sentences.