If you have one of the more recent iPods with a screen, you will know that while the video playback is pretty good, not many videos come in iPod format. If you are using Windows a useful solution is
DVDVideoSoft's Video to iPod Converter. It'll convert a whole range of video formats to various different sizes and qualities of iPod .mp4 video.
It's freeware, and while you do have to tell it not to install the Ask toolbar while you are installing it, all it takes is unselecting a couple of tick boxes. After that it installs normally and works just fine.
If you prefer to read text, it's not quite so easy. For some reason, iPods don't have an easy way of uploading ebooks. On the other hand, it is possible, using the Notes function. The problem is that Notes can't be more than 4K in size, which even for text files is limiting, and so the solution is to use the
ebookhood website. There's a slightly worrying message there these days, which implies it may be going away, but until it does it's by far the easiest way of splitting a text file into 4K chunks and building in the links so that you can navigate from one part to the next. Simply upload the file into the form on the page (go into advanced options to give the files a name, which will make it easier to work with) and the result is a zipped file for you to download, containing the separate Notes that make up the original file.
Make sure you've ticked the box on the Summary tab in iTunes that enables you to copy files directly to your iPod and it will appear as a hard disc in Explorer. Copy the unzipped contents of the file to the Notes folder (you can put each separate book in their own folder if you like) and then find them under Extras and then Notes on your player.
If podfic or other spoken word stuff is more your style, you may find listening to a string of long mp3s to be a pain. There is an iPod Audiobook format, which works much better - stored separately on the player and with a built in resume function on each file, even if you've listened to other things in the meantime. There's a really useful Windows
MP3 to Audiobook converter here, which not only converts mp3s, but also combines them at the same time, so you can put a whole book into one file.