I'll tell yee about the Hongi, (not to be confused with Hângi which is Maori for tastiness.)
This is a hongi. [http://kristinasworld.files.wordpress.com/2008/02/hongi.jpg]
It's a traditional New Zealand Maori greeting, a friendly one which is nice. It's meant to represent the ha, or breath of life, being exchanged and intermingled. In it two people briefly press together their foreheads and noses, (that is, they press their forehead with another's forhead and their nose with another's nose, I don't think you can physically press your forehead and nose together but I encourage you to try.)
Note: It is imporant not to be overenthusiastic and end up headbutting a big maori dude like I have done on more than one occasion.
If you want more Wikipedia's got a pretty nice description.
If you come to NZ and find yourself being welcomed onto a marae this is basically how you'll be greeted, (although nowadays it also accompanies a handshake.)
You can look into the Maori haka as well, that has a number of neat gestures that all mean various things, (including a personal favourite of mine that is basically a "my dick is huge and hard" boast.)
I'm pretty sure American gestures mean the same here in NZ as they do in America though, (don't believe Flight of the Conchords, we know what flipping the bird is and use it frequently.) I can't think of any that differ anyway.