Depends on what you want to do. Client side, server side, application. You'll find that many languages are rooted in other base languages and that you can easily learn more than one.
Personally, I know VBA, PHP, Perl, Python, ASP, AutoLISP, Oracle, MySQL, PostgreSQL, C++, C, Objective-C, Cocoa, XML, XHTML, HTML, CSS, Java, JS, Ajax, Ruby On Rails, *.NET - and those are just the ones I know "really" well lol