Alligators, gorillas, bugs and sharks. Lots of sharks. As ever I can't claim this is definitive, but you can't go wrong with any of them.
Alligator II: The Mutation
Unrelated sequel in which Joseph Bologna and Richard Lynch hunt an urban 'gator.
Moby Dick (2010)
Every bit as terrible as The Asylum's deliberately bad movies, but far funnier because it's trying not to be.
Night of the Lepus (1972)
Massive rabbits terrorise Arizona. Who thought this would work?
An obvious choice but Jon Voight is spectacular. See it for him alone.
The Last Shark (1981)
The first of two shark movies on this list that have struggled with US distribution due to 'similarities' to a certain other movie.
The extent to which nobody cared about this South Korean/US co-production is palpable and extraordinary.
King Kong Escapes (1967)
Giant mechanical Kong faces off against regular hairy Kong in a battle to the death.
Empire of the Ants (1977)
Joan Collins does her best with an absurd script and some of the worst visual effects ever committed to film.
Tail Sting (2001)
Giant killer scorpions take over a plane. See highlights from Tail Sting
TIE: Cruel Jaws (1995) and Shark Attack 3: Megalodon (2002)
It's a cop out but I don't know how to pick between these two. Cruel Jaws can't be released in the US thanks to its prolific pilfering of shark footage from other movies (including The Last Shark and Jaws). And Shark Attack 3's infamous visual effects & terrible dubbing make it hilarious. Now if someone could just make a movie in which these two sharks face off. See highlights from Shark Attack 3
Shark Attack 3