I couldn't resist and so here are mine:
"JavaMonkeyEngine: Yes, Monkeys live there too…"
"All your Monkey are belong to us"
And maybe we should put a coffee cup at the Monkeys mouth too…
ninjaboyjohn said:
"Monkey code, Monkey play"
I actually REALLY like that one, maybe just keeping the first line of that phrase -
"Monkey see, Monkey code, Monkey play"
I'll throw some in for the hell of it:
"Created by man, perfected by monkeys"
"jMonkey Engine... why? You wanna mess with an animal that flings it's poo?"
"We're not just monkeying around"
"When you're ready to monkey around" -- could be several variations of these
"It's not just for monkeys anymore"
"From our trees to your screen"
"Is that a banana in your scenegraph?"
"Because King Kong said so"
"Because King Kong said so"
Lets not be womanizers, so:
Because Jane said so
perick said:
"Because King Kong said so"
Lets not be womanizers, so:
Because Jane said so
:D
Could be Jane Goodall
chirstius said:
"jMonkey Engine... why? You wanna mess with an animal that flings it's poo?"
if there were categories that would get 1st prize for funny, sick and twisted :D :D :D :P :D
"Monkey see, Monkey code, Monkey play"
that one is pretty good.
Could even have a fun image that's a take on the see no evil, hear no evil, speak no evil.
"JavaMonkey! Ready to sacrifice himself for the greater good"
like the Spacemonkeys in FightClub, or You rename JavaMonkey in Space Monkey XD
mojomonk said:
"Monkey see, Monkey code, Monkey play"
that one is pretty good.
it is!
“Changing game development one monkey at a time”
slightly more boring, and slightly more descriptive than the options so far…
but slightly lame…
“The missing link in Java game development”
or just
“Because it has monkeys!!1”
I love the missing link one, or something based off of it.
What about "let monkeys do the hard work" }:-@
can be misunderstood but it is catchy.
"One small step for monkey's; one giant leap for java" 
Going to lock this in favor of the poll for now. If the options in the poll are not popular we'll re-discuss. 