Uke Uncle's aforementioned book is absolutely wonderful! Definitely get it!
There's also a book/CD by Heeday Kimura that is for standard tuned ukuleles, sopranos and concerts and such.
http://www.elderly.com/books/items/541-11.htm
Another good resource is any slack key guitar instructional video/book/CD by Keola Beamer, Mark Nelson and/or Ozzie Kotani. Its pretty simple to put the guitar arrangements into a playable version for ukulele once you understand the basics of slack key. You have to modify the bass notes for ukulele, but the melody lines stay pretty much the same.
In a nutshell, I'd advise to get Uncle Dave's book first. Then go for the Ozzie Kotani guitar book/CD if you're still craving more.
As for the baritone, yeah, there really are some great deals to be found on Ebay. I ended up with two baritone uku. One I keep in taropatch tuning, DGBD, and the other I switch back and forth between the various alternate slack key tunings. And of course we have yet to talk about where to find chords for those tunings, strings, and a whole plethora of cool stuff!
Slack key is a wonderful style of music. It really inspired me. You're on a very interesting journey!!