Very nice, currently underrated movie.
Nice drawings, pretty good animation and nice use of sound effects. Good use of stuff like balloons to convey the monkey's feelings, and a solid plot, which can be a rarity on NG.
Typing web addresses in reviews seems to be forbidden, though the screen I'm no says "no promotion of *unrelated* web sites," so maybe I can help you out a little on finding sound effect sites. A good place to start is Partners In Rhyme at partnersinrhyme dot com. My own method of finding specific sound effects is using Google and typing in stuff like "download sound effect police siren" or "download cartoon sound effects." It takes some sifting through unrelated sites or sites that try to sell you sfx CDs, but just bookmark all the reliable sfx sources you come across and you'll build up a nice archive in no time. Good luck!