I agree with what everyone says about Henle. I use it religiously. I also use Barenreiter (sp?), Durand, Boosey & Hawkes, Universal, and Vienna, and Presser/Paderewski (for Chopin). These are all very reliable sources, although expensive. If I can stand to afford it, I buy them and steer clear of Dover and G.Schirmer. Dover, in particular publishes everything under the sun. If you need something in a crunch, that's what I would get. However, I would not trust their sources, not to mention their binding (nothing stays open at the piano like a Henle). Anyway, I hope that helps.
Mike