Reddit reviews Lightroom 2: Streamlining your Digital Photography Process

Here are the only two I have read specifically for lightroom, I highly recommend both:

for workflow and basic functionality (workflow isn't as sexy as editing, but if you get a good system down, it will essentially become second nature and allow you more time for editing):

Lightroom 2: Streamlining your Digital Photography Process

For the creative process: (arcterex already mentioned this one.)
Vision & Voice: Refining Your Vision in Adobe Photoshop Lightroom (Voices That Matter)

Anything by David Duchemin is great, he also has a blog and some great ebooks

This is a good blog also:
http://lightroomkillertips.com/