Wildart has been working on an F# addin for MonoDevelop for use on all platforms where Mono runs. To quote

I just finished draft version of F# Addin for Monodevelop. This addin provides support of F# compiler in Monodevelop IDE. You could find new version of Monodevelop in Mono 2.0 Preview. Take a look!

The project site is here. Wildart has also been working on a NAnt task extension for the F# compiler .