Hey, I know exactly how you feel. I have to add extra arch support to everything I wear. Naot, born, clarks, dansko, all those brands that everyone else says have "great arch support" just doesn't work for me. The only brand of sandals I found that I don't have to add extra arch support to is Earthies. I have about 6 pairs and they are great. There is one style from them that DID NOT have enough arch support is the Santini. I had to return that one. I was sad because it looked so cute. So stay away from that one. But everything else has been good so far.
A style I would suggest is this. I have a pair and they work well with casual clothes.
http://www.6pm.com/earthies-teesi-black
Another brand you could consider, Merrell encore collection, and ONLY the encore collection. The shoe itself DOES NOT have enough arch support. But when I add this insole under their removable foam, the combination works pretty well.
http://www.amazon.com/Spenco-P.....038;sr=8-3
They have this style for the summer that is pretty sporty.
http://www.zappos.com/merrell-.....ilver-mist
P.S.- I got a size bigger to accommodate the extra insole.