Windows/Mac/Linux: Rip DVDs to your iPod with HandBrake, the latest version of the program previously known as MediaFork.
HandBrake can turn DVDs into iPod-friendly MPEG-4 or H.264 video files. It includes iPod, Apple TV and even Sony PS3 presets, but you can also customize various audio and video settings to your liking. (Needless to say, the ripped files will also play on Zunes and other devices.)
Windows users can choose between GUI and CLI versions; both require DVD43 to be installed if you want to rip copy-protected DVDs (the ones you own, of course). Also, be sure to choose the VIDEO_TS folder when you browse the DVD, and then select the "title" that contains the actual movie (it's usually the longest one). For Windows users in particular, HandBrake definitely makes easier work of copying DVDs to your iPod, though the overall process still takes a few hours.
Still in beta, HandBrake is free; it's available for Windows, Mac and Linux operating systems. —Rick Broida