DeadDude- Delphi is like VB in many ways. Like VB its built upon a decent programming language (Pascal was a bit of a dead language for a while with only a small following but since a few other compilers can be found now for Object Pascal its is starting to get a bit of a revival).
Delphi has RAD environment like VB, but like VB you really need to learn a bit of the underlying language to get the best from it (in case you didnt get it from the last bit, delphi sits on top of pascal). It is pretty simple to whip out a program in Delphi, much like VB, and you can also get Delphis younger brother Kylix for linux. Borland who made Delphi has discontinued development of Delphi as of last year, so that is a bit of a downside.
To get more info follow these two links to wikipedia.
Delphi or
KylixNephilim-You mentioned open source. I did mention C++ with MFC, but he's also looking for something he can pick up easily and comes from a VB background. MFC may not be open source, but you will find that c/c++ were the original open source languages (since thats what most *nix kernel were written in, and what most *nix software is still written in). Also just so you know Delphi is a RAD (most poeple refer to it as a language),the language is Object Pascal, and wouldn't you know it there is
GNU Pascal.
At the end of it all, there are alot of languages out there, and if you are willing to put in the time searching the net you can find how to write good apps in almost any language. Its really just (as is said in Ireland) much of a muchness. Take your pick to which suits you. (I forgot there is also python, perl, ruby, lisp, cobol, fortran, java.......

)