Pretty much everything that Team Rocket uses. They'd be great for levelling up, if it wasn't for the fact that they use the same Pokemon all the time! I'll make an exception for Ekans and Arbok, though, because they're awesome.
I'm not fond of the bug types or the Nidoran family, mainly because you have to battle them all the time in FR/LG (and probably R/B/Y as well). I get that Pokemon was inspired by real life bug collecting, but bugs didn't have to be THAT prominant. And as for the Nidorans, I just don't like 'em.
I also hate Oddish, but that has more to do with R/S/E, so...