I definitely want more Poison types. It's gotten to be my favorite as of late... I kinda wish there were more Poison-types with higher stats, specifically. Poison is the type with the lowest stats, now that Bug got upped so much. Ghosts also have low stats in general, but their immunities help make up for that. And I want stronger and more reliable Poison-type attacks! Like a physical move with 100 power and more than 70% accuracy.
Of course, Ice, Dragon and Ghost are pretty rare, so we need some diversity, there.