What's a good programming language to learn?

[Sir_GT]

Serious question guys. I'm basically faced with the opportunity to learn just one. Although it really is the entire language course. From baby steps to full soft-ap development.

Java?
Visual Basic?
C#?
Other? (Feel free to suggest)

My criteria:

Large market (either current or growing) for demand reasons
Platform flexibility/Can be applied universally
Developmer support by the "industry" (i.e. I can't learn a language that is supposed to be discontinued soon)

Fire away guys. I saved up for this, so I really just want to invest in the right one.

Although I'm familiar with webstuff, such as HTML/XHTML/DHTML/CSS/Flash Actionscript, I only have a fairly basic understanding of PHP and MySQL stuff, since most of my current work is really design-related, so if anyone thinks that those are better investments, feel free to point it out.