If you're going to take on VB
.NET, you may as well take on C#.NET. Because it's a "curly bracket" language (like C, C++, etc.) it looks better on a resumé. Plus, learning C#.NET is just about as hard as learning VB
.NET coming from VB5 or 6. The biggest downside is price. Visual Studio.NET gets pricey fast. Not to mention the volumes of books required to learn the thing. But, it's an in-demand language these days (since .NET is not a beginner's platform).
But I think your original question was "WHAT should I program?" not "What should I program IN?" In the past I've programmed programs with an educational bent: a database of the Roman Emporers or popes which showed how each of them died or salient facts about their reigns - the challenge in this was all UI and trying to top what's already out there; Spanish verb finders with database and scripting for regular verbs. Probably the best thing to do is try to outdo something that already exists.