This blog post by James Rowland Jones on a specific type of deadlock is so interesting that I have to share the link to it. Not only so other people read it, but in case I ever need to find it again in a pinch, I can easily find it on this post. James encountered a very interesting deadlock and provides a really in depth explanation including the use of an undocumented side of locking in SQL Server that you'd be hard pressed to find somewhere else online.
http://blogs.conchango.com/jamesrowlandjones/archive/2009/05/28/the-curious-case-of-the-dubious-deadlock-and-the-not-so-logical-lock.aspx
As an additional note, he mentions at the bottom of the blog post an upcoming SQL Server Internals book that he is co-authoring with Christian Bolton, Justin Langford & Brent Ozar with contributions from Cindy Gross and me. I am working on the Waits and Extended Events chapter in this book currently which has been quite a learning experience and has really changed how I look at problems in SQL Server and troubleshoot performance issues personally. More to come on the book when it gets closer to publication.
EDIT:
Apparently Jame's blog post was so interesting it sparked some other posts online as well..
http://rusanu.com/2009/05/29/lockres-collision-probability-magic-marker-16777215/