Here's a Dev Radio episode I did on TryFsharp.org, a simple way to test out F# in your browser without having to download anything. F# is an easy language to learn, but also remarkably powerful. You end up writing less code than with other languages, and your code is easier to reason about. It's cross-platform and fully open source under the Apache 2.0 license. TryFsharp.org contains tutorials you can go through at your own pace, perhaps over lunch. Using Silverlight, the site lets OSX and Windows developers run the compiler in their browser.

Here's a tour of the TryFsharp.org website: