BlackDan said:
Don't do Java. PLEASE.
Learn C/C++. No matter what everyone is saying there's still a performance issue with Java AND ANSI C/C++ is the most commonly used language IMO. Also I think C++ is easier to learn. The idea of Java is great, being platform-independent and all, but I don't think it's the best place to start.
There shouldn't be any issue with performance with a properly written Java program - yes, even the most efficient Java program is slightly slower than the most efficient one written in C/C++, but it shouldn't be any more than 5-10% difference in runtime, if you don't take into account the time to load the virtual machine, which only takes a couple of seconds anyway, which isn't an issue with long running applications.
Unfortunately lots of people come into Java and use things like List.indexOf or String.charAt without knowing what they're doing, or forget to initialize their Arrays or Maps to the correct size, and find that their program runs like a dog with three legs. On the other hand, lots of people come into C/C++ without knowing enough about handling memory allocation.
For instance, a colleague of mine wrote a program to parse a really large XML file (several 100 MBytes and tens of thousands of entries) that took about 2 minutes just to start. I rewrote it to take less than 5 seconds to start, because unlike him I knew how to initialize the data structures, and also realized that you didn't actually need access to all the data and only parsed (and cached) the individual XML entries when they were requested by something the user did.
Another for instance - a customer of ours wrote a C++ extension to some of our server software and started screaming blue murder when our servers started core dumping regurlarly, and refused to accept that the problem was in their code. Eventually they let us see the code and within minutes our C++ guys were able to point out three major memory leaks in a 100 line program.
Anyway, what language to learn depends on what you want to do. For webapps, Java/JSP or .NET/.ASP are the two defacto standards - except that Java/JSP is cross-platform (our webmail software runs on Windows, Linux, Solaris, AIX and HPUX without our having to modify anything), but if you're thinking of doing engineering, C/C++ probably is the best.