Microsoft has just released the F# CTP. The neat feature rolled up in this version is its integration with Visual Studio 2008!
Download the CTP from the following URL: http://www.microsoft.com/downloads/details.aspx?FamilyID=61ad6924-93ad-48dc-8c67-60f7e7803d3c&DisplayLang=en
For those who are not familiar with F#, check out the F# Developer Center.