As I recall, WP7 supports C# but does not support any of the .Net dynamic languages (Ruby or Python). Are any other programming languages besides C# supported? Could an app be developed using Boo?
Officially, only C# is supported so far. Unofficially, any language that can compile to a verifiable managed assembly (the verifiability requirement applies to all dependencies, too!) is good - so you should be able to use e.g. C++/CLI, F#, Delphi Prism...
Currently, officially supported is C#. In the medium term (although no time frame officially announced) will be full support for VB.Net & F#. In the longer term will be official support for dynamic languages (IronRuby & IronPython) - although expect a restriction in what you can do with these languages due to marketplace restrictions.
The CTP of the Visual Basic tools are now available from http://www.microsoft.com/downloads/en/details.aspx?FamilyID=a808a69d-6119-47b7-b858-262be5c49915
F# is supported on the phone. The templates are not baked into Visual Studio yet but are available from this blog entry by Don Syme
If you can compile it down to a .NET CF assembly, you could probably hack it to work - there's nothing explicitly stopping other languages from being used.