Gosh, I've already heard some jokes hear I've never heard before.

But, I've always loved the "uh oh a plane crash...you know what this means...hippos!" joke. I love non-sequitir humor.
Here's a few of my favorites that haven't been mentioned yet. These are paraphased, and of course depend a lot on delivery, but here goes:
"Here with the lions in the African velte we see the first law of the Jungle....don't be a zebra!"
"There's smiley, our 10-foot crocodile...he's always looking for a hand-out. And there's his girlfriend Ginger. Heed this warning...stay away from Ginger...Ginger snaps!"
"As we approach the end of our journey you'll note there's a dock on the left and a dock on the right. That's what we here at the Jungle Cruise like to call a paradox."
SkierPete