I'm a big fan of simple but good ideas, and "B.O.B." (I'm still not sure what the acronym means) from Hopscotch Technology is a pretty good one. Simply put, it's a lock box for a power plug. You plug whatever media device you want to restrict your child's use of (like a television or video game machine) and set a specific amount of time you want to allow your child to use the device. The kid logs into the box with their specific number, and the power to their TV turns on. You can also allow or disallow blocks of time too.
It's not just that I'm incredible thankful that such a device didn't exist when I was a kid (although I am), and it's not because I'm a parent now that I can imagine using such a device someday. It's my experience playing Halo 2 on XBOX Live that makes me wish more parents had this. If some of those kid's who I'm constantly losing to spent as much time on their homework as they do playing Halo, we'd be raising a generation of freaking super-geniuses.
When the hell did I turn into such a crotchety old man?