Yeah, probably learn Java. Or C++, but it's complicated and less important now than it once was. Objective-C is good for iPhone, Ruby or Python + Rails or Django for web development (these are trendy right now).
But your best bet is Java. Also, if you have enough languages on your resume, in enough different areas, good employers will expect that you can learn a new language in a week or two.
Java isn't even that terrible, it's a stupid frustrating language in a lot of ways, but that's because it's designed specifically for large enterprise projects with hundreds of mediocre programmers. And for that it works great. Also, the JVM is very fast now, almost as good as C++, and cross-platform.
If you want to learn a "good" language too, why not learn Java and then Clojure, which is lisp but integrated with the JVM and Java libraries.