As stated… Gaming servers like Minecraft servers, and other future game servers like Cube World servers and whatnot. Gaming clients for different MMORPGs, and graphics rendering like creating custom maps and characters and whatnot for different games.
Added (1). Oh and programming games and programs with different languages.
If you want to play games at a good resolution: Go for a good GPU
If you want to code (so compiling) and video rendering: Go for a good CPU
If you want to host servers: Go for more RAM (and a decent CPU)
If you want it all, get it all.
If you're not sure what to buy, look for things within your price range and look for benchmarks.