Bartlett Publishing has put together several lists of books available from many various publishers which are essential reading for anyone interested in the topic. Check them out today!
You can view the articles from the blogs which preceded these at the following URLs:
Blocks is a new feature of Objective C that was announced roughly at the same time as Apple announced Grand Central Dispatch. I haven't had the time to look into it thoroughly, so I'm sticking my bookmarks here for future reference: