Today, HD merged in an amalgamation of windbg tools and plugins with a funny name into the main metasploit tree. We've been working on this collection for awhile now, and currently it represents (I think) a good step towards turning windbg from simply a good debugger into a powerful platform for exploit development.
The work that's currently released includes:
tenketsu - the vista heap emulator/visualizer which allows you to track how input to a program effects the heap in real time.
jutsu - a set of tools for tracking buffers through memory, determining what is controlled at crash time, and discovery of valid relative return addresses based on it
mushishi - a framework (with examples) for the detection and defeat of anti-debugging methods.
Used in conjunction with metasploit, jutsu in particular can significantly speed up exploit development time as it understands and makes use of msfpattern buffers natively. The README file can be found in the tree at external/source/byakugan/README and details functionality, usage, build, and installation. For the slides from the preliminary release at toorcon seattle, go here.
Currently we're looking for more suggestions for functionality. Anything that you do commonly and think may be automatable is up for discussion.