I'm 5'9", which is not super tall, but it's still tall enough to find certain stores a nightmare to shop in when it comes to finding clothes of a decent length (*cough Forever 21 cough*). Here are a few favourite brands I find are kind to those with longer limbs...
Most of Gap's jeans come in three sizes -- regular, petite, and tall -- and believe me, their "tall" sizes are long (I actually only need a regular length myself). I find their sweaters, dresses, and coats are also very generous in terms of length.
2. J. Crew
J. Crew's Creative Director, Jenna Lyons, is over six feet tall, and the brand's most famous patron, Michelle Obama, is 5'11"... needless to say, this is a store that caters very well to taller women.
While I don't own any trousers or skirts from Dynamite, I find this Canadian brand is surprisingly great for length in things like blazers and cardigans.
This British high street staple has a Tall section actually in store, which I appreciate (most stores that have tall sizes only carry them online). However, a word of warning: this line caters to women 5'7" and taller, so if you're 6"+, you might find some items are still a little on the short side. I've found that some of their supposedly "Tall" dresses are not particularly long, but you can definitely notice the difference in things like sleeve lengths.
5. Banana Republic
Part of the Gap Inc. company, BR is a great place for both tall and petite women to check out. Most locations have a Petites section in store, but the Tall range can only be found online (unfair but at least they have one, I guess!). However, I find that most of the regularly-sized stuff found in stores is actually lengthy enough.