My brother listens to audiobooks on his iPod when he can't sleep -- as he's gotten older he's started to suffer from insomnia, and now I'm developing the same problem. So I'm getting interested in audiobooks too.
I have a bunch of tapes here that I made off the radio during Terry Gross's interviews on Fresh Air (National Public Radio); I'm going to convert those to MP3s and put them on my iPod. I believe you can buy and download Fresh Air interviews from audible.com as well...they used to be available on iTunes but I don't see them there anymore, at least not in the Canadian iTunes store.
Also, free MP3s of TED talks (http://www.ted.com/
) are available for downloading; there's some really fascinating stuff on there, although the MP3s sometimes don't capture it all; you're better off downloading the QuickTime files and watching them (which I guess you can do if you have a newer iPod).
Listening to interviews and lectures is a great alternative to novels: they're shorter and usually very thought-provoking.