MythTV

This is a free Linux-based Tivo alternative (well, not exactly free--you need a PC to run it on, but you can build/buy one for pretty cheap, especially since Myth apparently runs on down to a 500 Mhz single processor box). In addition to Tivo functionality, Myth has some really nice features, like automatic commercial detection/skip and the ability to actually move the programs to another device (like an iPod). You can also use it to rip DVDs ono the PC and watch them just like TV programming.

Very cool!