What kind of game do you want to make? That really drives the answer.
If you're wanting to do this as a career, the big-name languages are the places to start. C and C++ are used for a huge number of mainstream games out there. Java also has a fair number.
If you're wanting to be an indie developer, you have a wider range of choices. ActionScript (Flash) is a solid choice due to its wide support and ease of user use. Any of the scripting languages (Python, et al) are decent choices, though any interpreted language will be slower than a compiled one.
If you're doing it for the hell of it, pick one you want to learn.
C / C++ are the big daddy languages that very many other languages base themselves off of. You should have no trouble finding a job if you're good at these. They're fast, but dangerous: they let you get deep in the nitty-gritty, but you can also shoot your foot off if you're not careful.
Java is the other "big" language that you hear a lot out of. It'll do more to try to keep you from doing something stupid (it's garbage collected, strongly typed, etc), but it has more overhead in exchange.
I don't know Python, but it's very popular for scripting as well as larger projects. It is interpreted, meaning it's easier to test on the go and will run on anything that has a python interpreter written for it (which is practically any system.) You'll see a performance hit, though.
Ruby is an up-and-coming language that's said to take the best features of Python and Perl with a few improvements of its own, and with Ruby on Rails has strong web support.
I've seen several smaller freeware games in FreePascal, which is reminiscent of C, and not too hard to learn.
I'm going to throw in a plug for D. It's not mainstream, but it's a successor to C written by a compiler writer. It has all the strong features of C and C++, without the legacy issues of C++, plus more modern language features that C/C++ lack.