(Apologies for shameless self-promotion!)
In several of my posts, I mentioned the book on formal languages that I've been working on for the last few years. I now have a draft of the book ready for (moderate!) public consumption, which is now available here. The two final chapters are still missing, but the draft is already something of a coherent whole, or so I hope.
Many people have kindly expressed their interest in checking out the material, hence my decision to make it available online at this point, despite the fact that it is still a somewhat rough draft (references are still a mess). Needless to say, comments are always welcome :)