When I pick up a language, I try to learn at least 85% of its syntax/design patterns (including the standard API, although it takes a long time to pick up a sizable knowledge of most out there).
As
>>2 says, get better with what you already "know." C and Python are pretty powerful (one good for systems programming, the other good for high-level OOP).
Anyway, 3 languages:
Lua - Big for integrating in to games. Very light, and will teach you the functional way of thinking. You can glue it to C with custom or SWiG-generated bindings (one C function call will be like 1000 lines of code if you hand it to SWiG... but it's godly).
Ruby - Lua on steroids. Lua reflects its origins in being tied closely to C through its small standard API and primitive data types (...and lack of stable threading), but Ruby breaks off that through being fully object-oriented and the introduction of a sizable standard API.
Perl - I will never fully learn this language, because it's so fucked up. That said, knowing a decent subset of it necessary to get things done fairly efficiently is highly beneficial. Perl's real power lies in CPAN. I find myself gluing perl scripts to ruby a lot these days.