BitC, a project started by Jonathan Shapiro of Coyotos project fame and briefly associated with Microsoft's Midori project, is a systems programming language that supports garbage collection but also allows the programming of critical sections of code in which garbage collection is not permitted to take place.
From http://research.microsoft.com/pubs/52716/tr-2005-135.pdf:
I appreciate that Microsoft Research is saying "why not?" rather than "why?". Singularity is a fascinating OS and I hope it, or some derivative or something like it from someone else, eventually reaches the mainstream market.