I don't know if you're familiar with mono, but it's some sort of framework to be able to code/run C# on non-windows systems. Someone succeeded in porting it to Maemo, but I don't know what it's current status is.
Find the thread about it here.

Edit: downside is, if anyone wants to use your application, they need to have mono runtime installed... (previous poster was faster than me and might have suggested a better alternative )

Dries