World of Goo was a pretty big deal on WiiWare and PC a few years ago. I pretty much got sucked into the hype and bought it pretty quick. I heard they've also made versions for Mac, Linux, iPod touch, iPhone, and iPad.
The concept for World of Goo is pretty simple. Build your tower of goo power to complete your objective.
My favorite was the frog stage, but I must say they do get way too hard later on. But it's still a fun game for anyone to enjoy.