It didn't take long...

In fact, the film Snakes on a Train actually came out three days before Snakes on a Plane. That's right, the knockoffs started before the film came out. Naturally it's straight to DVD, and by all accounts, it's a pretty bad film, but I have to admit that I'm intrigued by this tidbit from Wikipedia:
The film features former WWF wrestler "The Iron Sheik", in a major role, although he appears under the pseudonym Ronald "Bubba" Sparks.
Score. I don't know about you, but I'm still holding out for Ostriches on a Hovercraft.