If you have a TiVo, there are several apps in the App Store that can make recording and playing your favorite shows just a little easier. While none of them allow playback on the iPhone or iPod touch themselves, they're still useful tools for TiVo-holics.
For those with TiVo Series 3 boxes, DVR Remote turns your iPhone or iPod touch into not only a remote control for your TiVo, but also a much easier way to enter text, compared to using the remote. There is a little bit of setup that you have to do on your TiVo before DVR Remote works, but once all the devices are talking to one another, you can view Now Playing information and select favorite channels straight from this app. DVR Remote (App Store link) is $2.99.
For those with Series 2 DVRs (like me), DVR Shows behaves much like the NowPlaying dashboard widget (sans downloading capability). DVR Shows lets you browse the contents of your Now Playing list and view program details. DVR Shows (App Store link) is 99 cents.
If you want to take advantage of the TiVo's remote programming option while browsing your media guide and program schedules, the current version of i.TV supports that function. Some testers have had mixed luck with the capability but your mileage may vary. i.TV (App Store link) is free.
Last but not least is DVRPics, a utility that lets you show a picture from your iPhone or iPod touch's Photo repository on your TiVo Series 2 or newer. (Right now, you can only show one photo at a time, but the developer promises a free update to create slideshows.) You can also take pictures using your iPhone, and immediately display them on your TV. DVRPics (App Store link) is 99 cents.