Ran across some references to the Glagolitic script, so I have to post them, plus some others I knew of to round out the collection.
For those unaware, Glagolitic is the script developed by Cyril and Methodius in the 9th century so that they could translate stuff (i.e. the Bible) into Slavic languages. And it is a very cool script. If you're deep into textual criticism, it could pay off to have some familiarity with it.
If you're really interested, perhaps Horace Lunt's Old Church Slavonic grammar (amazon.com) might be a place to start. Note I've not seen this, it is just the most accessible/affordable English language OCS grammar I've seen to date.
So here are some links.
Enjoy!