Look into that new Tamron 150-600. Dylan's links go to thread discussions and by all accounts its a tremendous lens for entry level wildlife photography. I started out with a 400 f5.6 on a crop (40D and 7D) and its great but if the Tammy had been around when I was first getting into birding I would have gone for that in a heartbeat. I mean seriously, IQ that matches or beats Canon's 100-400, an extra 200mm on the long end and IS for just over 1000USD. What's not to love (other than the slow aperture at 600 but, eh, tradeoffs)?
I read both threads on the Tamron 150-600 and developed a real interest in buying it but can't locate one in stock anywhere. Thought about buying one from Adorama or B&H but I would get the most use out of it while on vacation and my spring/summer trip may arrive before the lens would.
Fall trip I probably won't need it so it may be another year before I get one.