Aipom and Ambipom
I believe Aipom here was our very first indication that Pokemon would ever repeat animal bases it's used in the past, this being our first primate since the Mankey line, and certainly full of personality. The hand on its tail isn't the most imaginative or innovative gimmick I've seen in a pokemon, no, but I really love Aipom's face. It's that perfect rat-bastard cartoon monkey face. As a non-evolving pokemon, however, Aipom would be swiftly forgotten by most, remaining one of those overlooked, one-off oddities for years to come.
Aipom would finally evolve in Diamond and Pearl, into the larger and stronger Ambipom, now with two creepy udder-like tail-hands! There's not much else to say about Ambipom, except I kinda like its skeletal nose-hole, basically indicating that this is one of those horrid little snub-nosed monkeys.