I used to use Liz at paintedj.com, she did lots of nice things at reasonable price. I am now using kimberlyskreations.net, as I have known her for a while and she is local to me. It really depends on what you're looking for. You can get a plain button up for $35 or a $5,000 jacket.
Low range- Schneiders, rods, hobby horse.
Mid range- lisa nelle, paintedJ, woods western
High range- kimberlys kreations, showgirls (retailer of Lindsey James, Trudy, etc), Connie's customs, All that show clothing, show me again, showtime.