Resources for understanding SQL Server locking and concurrency?
Best book on the subject, and the most complete resource, is Kalen Delaney's SQL Server 2008 Internals. You really can't do any better. Another good book on the subject is Chris Bolton's SQL Server 2008 Internals and Troubleshooting. I don't think it's as complete as Kalen's book, but it does cover things pretty well, especially around locking and concurrency.