I listen to a lot of audiobooks and just did a search for some new sources and found a site that must have been there a while but it's new to me:

http://www.podiobooks.com

I sampled a few books and seems like some of the readers (all of the samples I listened to were the authors) are OK and some are, well, straight out of Ferris Bueller's science class...anyone....anyone...pretty much a droning mono-tone read.

One neat thing is the content seems free or at least you can donate is you enjoy a book. Plus the books are serialized with podcast feeds...could be a fun source of something different from other content options. The audio plays fine on my N800.

Not always great content but it's a reasonable model for business...like it and ya pay for it...don't like it, don't pay anything...or at least you can pay what you can afford.

Here is a great audio books site which is totally free:
http://librivox.org/

They have over a 1,000 titles!

I been listening to podiobooks for a while now. Mostly science fiction and fantasy.
I would recommend:

Shadowmagic (Very good)
Billibud Baddings and the Case of the Singing Sword (Very good)
The Pocket and the Pendant (Very good and child safe)
Nina Kimberly The Merciless
The Flown Sky (Children Orientated)
Under the Stairs (Good story if you don't mind the narration style)

<Edit>Just finished "Singularity". Very good sci-fi novel. </edit>

The hard part with Librivox if finding what you want. The Sherlock Holmes books are there although the narration quality varies.

Are you listening on your N800? If so what app are you using? I have yet to find a player on the N800 with a "resume", or "bookmark" function. Without that it is not possible to listen to Audiobooks without reripping to short files.

The files are all standard MP3's so can be played using any media software. Unlike audible, they are released as chapters so you don't need to split them yourself.

The latest versions of Canola (from Beta 6 onwards) are supposed to offer a resume from previous position option, but I haven't tried it myself as the lack of a "download all new podcasts" option means downloading my daily podcast collection takes too long. It also tends to crash during downloading.

For playback I tend to use MediaBox as media is arranged by directory rather than mp3 tags. It also offers the kinetic scrolling found in Canola but in a much lighter and snappier package. Otherwise I just use the standard media player.

Another site worth a look is http://escapepod.org. This is a science fiction short story podcast with a new story each week. There are almost 150 stories in the archive. If you prefer horror they have a sister website http://pseudopod.org and from April there will be a dedicated fantasy site http://podcastle.org

I have tried Canola and it has no resume or bookmark feature. Ditto for mplayer, mediabox or the media player that ships with the Nokia. The media player has a sort of bookmark feature that only works with internet streams. I am frankly surprised not one of the apps that plays mp3 files on the Nokia will facilitate listening to audiobooks. I never thought for a minute when I bought the device that this would be the case. They even sell audiobooks on emusic now so it isn't as if no one has heard of the practice. If someone is out there bookmarking their mp3 audio files on a Nokia Nxx I would love to hear how you do it.