Convert .NET is an integrated, powerful, multi-purpose conversion and developer tool. Features: C# to VB and vice-versa, LINQ tester, Encryption/Decryption, Regular Expression tester, Base64 Encoding/Decoding and Full-text translation.
This would be fantastic as an extension. But as a stand-alone application, the convenience is lost. I won't likely be using it every day, which means that when I actually need it I won't remember where it is, or I'll have to sift through a bunch of other junk to find it.
All that to say, since it's a stand-alone application, just using a browser to Google what I'm after is more convenient.
Consider turning this into a collection of dock-able windows within Visual Studio and you could have a hit on your hands. I'd pay for that. Open-source it or add a pluggable API so people can add other kinds of conversions. That would be brilliant.