I think I've seen this thread before...
Jynx. Jynx definitely needs more love.
I think Tentacruel is often overlooked. But the one I actually like is Bibarel. I used one in Pokémon Pearl. A lot of people hate Bibarel for whatever reason. It's not the best Pokémon in the world, but I like it, plus I was pleasantly surprised when I found out it was a water type as well.
It is loved, it's a great Pokemon in RU and is viable in Ubers though I'm not sure about the usage statistics.
Furthurmore I'm pretty sure every Pokemon has there own big enough fanbase, after all were just one site compared to the other loads of Pokemon fans out there.
You're not a competitive player, are you? Tentacruel is everywhere in OU and it's very annoying with its Dream World ability.