George Jardine, the Colorado-based photographer and former Pro Photographer Evangelist form Adobe Systems was in at the birth of Photoshop Lightroom. He knows it backwards and forwards. Better yet, he knows how to explain its nuances better than anyone I've found. George has just released the second set of tutorials on Lightroom 4, this on the develop module. (Previously, he released a series on the Library module.
They are of high quality, full of valuable information, and reasonably priced. Find details and other tips on his website.