I found one before but can't find it now. It was a page where you put in your move types, e.g. Grass and Water, and it lists which pokemon you get "not very effective" against.
Grass and Water, for example would list Dragonite, among others.
Thought I may as well answer this now, because I made my own after asking here.
Pokemon Type Coverage calculator
If you want something where you can put in the type mix of a Pokémon and get back an effectiveness chart, try this: http://www.psypokes.com/dex/typeanalysis.php
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