I've just finished reading through a new book on lichens, which I thoroughly recommend:
The Lives of Lichens. A Natural History, by Robert Lücking and Toby Spribille (Princeton University Press). It's not an identification manual, but a wonderfully illustrated introduction to lichens, their biology and their place in the global ecosystem. Available from all good booksellers (and some not so good, doubtless) - and not at all expensive considering its content.
Enjoy!
Paul
