As I mentioned in a recent post, Windows Vista has new built-in support for deadlock detection. At the time, I couldn't find any publicly available documentation on this feature. Well, I just found it:

Wait Chain Traversal
Wait Chain Traversal (WCT) enables debuggers to diagnose application hangs and deadlocks. A wait chain is an alternating sequence of threads and synchronization objects; each thread waits for the object that follows it, which is owned by the subsequent thread in the chain. Read More.

The new APIs OpenThreadWaitChainSession, CloseThreadWaitChainSession, and GetThreadWaitChain permit both asynchronous and synchronous detection and response. MSDN also has a fairly detailed code sample that uses the new APIs to print out the wait chain for all threads in a process.