Just my suggestion... you should put all accepted suggestions in the first post so new people know. There not going to read every post....

My gym suggestion
Bug (already know this was mentioned! and bugs are stronger then you think... or at least butterfree is!)
Fairy (obviously.... mentioned before)
Dark (cause Dark ones are awesome)
Water (cause there has to be a water)
Poison 
Flying
Thunder
Psychic

These are my suggestions... also I think we should all be new trainers so our pokemon aren't OP. Just shooting ideas.... also we kinda have to decide who's gonna be the gym leaders.... are they gonna be npc's? Make a map on paint or something after we decide the gyms. a new world would be better then an existing one.