In case you're interested in something a bit more substantial than online lectures you might find the following of help. Rovelli's book is a good read, dealing, as it does, with many of the basic topics. It should be noted, however, that it's philosophical in nature, and most certainly isn't a textbook. I also have severe disagreements with several points he raises in the book (indeed, he makes more than a few claims which are patently false). Nonetheless, it's worthwhile getting hold of a copy if you're serious about learning this stuff.
A more comprehensive book is Thiemann's
Modern Canonical Quantum General Relativity. It's comprehensiveness comes at a significant price though: it's much more appropriately viewed as a reference work and
not as a textbook. Thiemann has an annoying habit of using terribly nonstandard notation in places but his presentation of the material is usually superb. There's also a large number of useful appendices if you need to brush up on your differential geometry, topology, and so on.
My personal favourites are the following three:
- Baez & Muniain, Gauge Theories, Knots, and Gravity;
- Ashtekar, Lectures on Nonperturbative Canonical Gravity;
- Kiefer, Quantum Gravity.
Of the three, Baez & Muniain is certainly the most readable. If you're familiar with Baez's
This Week's Finds... series you'll know he has a particular talent for apposite, chatty, and insightful explanations, something which shines through in this book. It may perhaps be the best introduction to the area.
Ashtekar's book is pitched at a considerably higher level. In particular, he dives straight into a discussion of the new variables, so if you're not familiar with this material you'll need to learn this first. Still, it's a book that everyone who works in the area has/should have.
Kiefer's book is my personal favourite. It's not restricted solely to LQG (although his discussion of this
is very good; he also covers Regge calculus and dynamical triangulations, black holes and quantum cosmology, and a cursory treatment of string theory. His discussion of the Hamiltonian approach (which is what you're really interested in when looking at LQG) is superb, cutting out much of the extraneous and irrelevant material that you'll find in, for example, Rovelli's book.
Hope that's of help.