A type coverage calculator would be a really cool and unique feature that could set the site apart even more from others. By this I mean you enter in four types of moves, and it'll give a list of what pokemon it isn't super effective against. So for example, say I have a pokemon with the moveset of Ice punch, thunderbolt, psychic, and Close Combat. You would choose from the 17 types and pick the following:
Four types: Ice, Electric, psychic, fighting
It would give you a list of pokemon you can't cover with it, so you know what to be ready for. In this case, Metagross would be one of the pokemon that comes up on this list since none of these moves are super effective on him, so you know to be ready should he come up in a battle.
It just seemed like a really nice idea.