Has anyone mentioned Free Pascal? It has an IDE and it can virtually do anything and natively with practically any CPU or O/S. For GUI applications you can use Lazarus IDE and practically most widget sets. Its fully open sourced.
It has a rich ancestry with Delphi and Turbo Pascal, with tons of open source libraries.
Easy to learn, readable code, object oriented, and simply rock solid fast compiled native executables like C, or C++.
I am thinking of making a bitcoin client port to Lazarus, if only I had some time...
There's a lot to be said for the Pascal based languages. They teach you good practices and principles. You can achieve 99% of the speed and efficiency of compiled C without the high chance of things like memory leaks.
The only problem is that no one really uses Pascal out in the real world, as C-syntax won the battle for popularity. And unfortunately, the Pascal high-level syntax can be confusing when shifting between languages (all future variables having to be declared at the start of functions etc.)
I'd definitely recommend Pascal/Delphi as a language to learn if you want to learn about programming. But don't expect to be contributing to projects any time soon. It's a shame, as it's a good language really.