Free GM Resource: Open Game Art
I was about to completely give up on a post today but decided to look for a specific sound effect I was hoping to use with my soundboard and I came across a pretty decent free resource. OpenGameArt.org is pretty much exactly what the title says, a collection of "open" art for games. While it seems clear that the art is for video games, a quick search of the sound effects tagged as "RPG", revealed several hundred sound effects. There has to be a few goodies in there to borrow for in-game sound effects.
I did notice that few sound effects would be sound-board ready as they really need to be unzipped and possibly converted over to your desired format. You might even need to get creative and combine some sounds & effects, either in the soundboard or with a dedicated program to make them a more usable length. For example, a hit sound might be half a second, but if you combine it with some "whoosing" sounds and a grunt or two....it might work.
Of course, YMMV.....