I haven't gotten into the details yet, but Books for Mac OS X looks very promising. I really need to get my conjuring books cataloged (which I have been collecting since 1978) and I really like that Books can export to XML.
Not that I'm an XML-is-the-magic-pill sort of guy. It's just that I've started many cataloging efforts over the years, only to get frustrated because my data is locked into some undocumented format. XML avoids the problem in almost all cases. (That's why I like Tinderbox for note keeping, too.)