I've been reading Paul Chafe's The Ark trilogy (two books out so far). It's "yet another" generation ship book but he's taking it much more seriously than many before. His ship design is very elaborate and he's even got
a site with the description. What's fascinating about the books is the look at possible social development in a ship that's traveling for ten thousand years and how the builders had to anticipate them (successfully or not). The fist book's part up to the launch was a bit boring and took me several tries to get past it but I'm glad I stuck with it, because second part and the second book is much more interesting.
The books are available from Baen's Webscriptions:
Genesis and
Exodus: The Ark.