Many of the Kindle 3 reviews overlook the fact that the Kindle is also an audio-book player. It plays MP3 files in the order you add them, which solves the “filename sorting” problem prevalent on desktop PC media players when the book comes without a playlist. And with 3Gb of storage to play with, storing a 600Mb audio book shouldn’t be a problem. Although battery life might be — I’ve yet to see a good battery test review where they look at life during audio playing + screen reading.
Want to test the Kindle 3′s audio book capabilities? There’s Librivox of course, which has a growing bank of free amateur-read audio books. I might recommend the classic short-story “The Cats of Ulthar” as a first “test my Kindle” download (although the reading on Archive.org is much better). Librivox’s search and site navigation leaves something to be desired, but the combined audio book search-engine Librophile searches their site and many more. Also have a look at Project Gutenberg’s human-read audio books pages.
For a more ambitious test, Amazon is currently offering you two free audio book downloads, if you sign up for your free 14-day Audible.com trial. Watch out though, as they want your credit card details and the fine print allows auto-renew unless you cancel before the trial ends (not after). Also be aware that there’s no preview of which books are available for the free download — it might be limited to popular fiction, for instance — which won’t interest non-fiction readers.
There will also be spoken-word podcasts for whatever your specialist niche interest is, although you no doubt know better than I what those might be. You might also check to see if your favorite authors have released any free ‘taster’ audio stories on their websites. There are also some quirky genre sites — or instance, the car maker BMW offers free classic stories in the crime/thriller genre. The fans at Old World Radio offers public-domain radio dramatizations from the 1950s, including classic science-fiction stories from the likes of Ray Bradbury, Asimov, and Simak. The H.P. Lovecraft Literary Podcast offers free full readings of classic Lovecraft stories, by proper actors.
Also have a look at the JURN Earworm search-engine, which lets you search just for intelligent speech radio (BBC, NPR, etc), intellectual podcasts, open courseware and the like. Some of these stream, some can be downloaded.