I'm a big fan of ebay
I recently got some new breeches and a saddle pad from horseloverz. They and Dover tend to have great deals on things.... but shipping can be high. I love smartpak because of their flat shipping rate and pretty much any place that offers free shipping! AdamsHorseSupply, Farmhouse tack, Equusnow, Equusunlimited, etc. I've ordered from them all!