Look into the Ergotech Freedom Arm. I actually use one on each of my U2715Hs. Incredibly solid full range of motion arms that don't actually break the bank at all. Rivals the Ergotron and Humanscale ones for quality (have had experience with the Ergotron arms before).
I just purchased a Loctek for my 34" Dell and it is impressive. I got it from Amazon, but it is not cheap, $145. It does have two different mounting brackets, which is nice and it is very well made.
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