Between the Werrd contest and a few other threads, I’ve seen the term “banger” being used. I Googled, I searched this forum, but there doesn’t seem to be a definition easily found.
I’m assuming from implication that it means… er… a fairly simple trick that you know you’re not going to screw up and can execute with impressive speed or style…? But I’d like to hear an actual definition instead of creating one for myself. 
I’d say it’s the opposite. I don’t know for sure but a “banger” sounds like the mindblower trick. The one you do that no one else does, or the one that’s so hard many people won’t try it because it’s too risky.
I’m guessing that their contest is basically a “big air” competition, asking people to do their most amazing trick.
insert dirty joke here
XD.
Haha.
But seriously, a banger is a trick that really gets the crowd going, like a really cool bind.
Take a look at my video called The Color Purple, there is a banger at the end of that.
Excellent definition found here:
http://yoyoexpert.com/forums/index.php/topic,49850.msg488985.html#msg488985
^ That link really does a great job of defining a “Banger”, but just my added two cents…
I wouldn’t want to say that “banger” came from skateboarding, but that is definitely the first time I heard it used and I’ve been riding/skating for close to 8 years now. I like to think of a banger as a trick that really comes out of nowhere and catches people off guard. It hits hard and really makes you want to rewind time (or youtube) and watch it again and again.
Awesome, thanks for the replies. Glad I asked; it’s the opposite of what I thought, as stookie also guessed!
As stated, I will confirm it is something really awesome looking or sounding. I’ve heard it used to refer to a lot of rap songs. If someone likes the way it sounds, “That’s a banger.” I’ve heard it used in other contexts too. If the slang ever goes over your head, use urbandictionary.com, and while it’s not always so accurate, it helps.