freesound(dot)org can be a good one, but you have to make an account to download from it I think.

youtube can be good as well. I've seen people upload videos of sound effect reels, so maybe you can download those via youtubemp3 or something

i found a couple of sweet sfx from some stickfigure animation resources forum and i've picked the ones i find them useful in some way or another. but, note that importing these sounds would lead to SFM not being able to play said sound. my suggestion would be to have a video editing software like sony vegas to help you out

http://forums.stickpage.com/showthread.php?37139-One-Stop-Shop-Sound-FX-Resource-Center-downloadables

http://www.hyunsdojo.com/community/viewtopic.php?f=21&t=580

http://www.hyunsdojo.com/community/viewtopic.php?f=21&t=1978 (this one will lead to Pepper's mediafire site, the user has a lot of folders so just click through and browse it. news from the forum told that a new pack is coming out but it would be in a few day or so)