>Our clients are asking for some applications over the web, so this is my question: which is a better solution for small projects: ASP, Visual C# or Java?

That depends. First the question could be: ASP, ASP .NET or Java as C# is just one of the languages you could use with ASP .NET

That said, you could have also asked for Cold Fusion for example or, this being a VFP Forum, you can also consider VFP with tools like Web Connect, Active FoxPro Pages, or several others.

The correct answer depends on many factors.
What server are you gouing to run your web under? IIS? Apache?
What OS? Windows? Unix? Others?
What is the skillset of the developers you have for the project?

Java is nice, but complex and IMO slow. Is it RAD? Are there any good tools for development? Don't know.
ASP .NET is better than ASP. It is what ASP should have been. Nonetheless, if you have VBS and ASP expertise in house it is still a decent choice. I have happy customers of my ASP+VBS web sites and the same with my VFP+Web Connect.

In short, it is not possible to give you a clear cut answer w/o information.