I'm about 6' tall and feel your pain! Every time I see these leggings, my heart skips a beat--I love them THAT much. But there's no way they're long enough.
I added the Betsey Johnson jacquard sheath dress, from Angie's list, to my think-about-it list. It looks like it's awfully close to knee length on the model. Sometimes there's enough hem to let out and make something work for us tall girls.
A few other resources for tall dresses, besides those Lyn mentioned, are J. Crew, Banana Republic, Land's End, Long Tall Sally, and Top Shop, which has a large selection of tall items. For all of them except Long Tall Sally, you have to order tall sizes online.
Hope that helps, and good luck!