Well, aside from the internets, you should look through some of the games you have, if you want to get sounds from them.
For instance, through a little bit of experimenting, I found out that WinRAR can open the files for most games, and often the sounds are contained in these files in the .wav format.
And, if you have any Steam games you want to rip sounds from, I suggest getting GCFScape and ripping the GCF files apart for all they're worth.
But the internet is good too.