Cavalleria Toscana is by far my favorite! All it's clothing is absolutely gorgeous and of the highest quality. However it's a bit overpriced!
Kerrits is also great and not so expensive, plus I find their breeches are very durable.
Hope it helps!
I second the vote for Kerrits. I also really like Tuffrider, Ariat, and Tropical Rider (my fav breeches). Even though I don't have any of them, I've also heard good things about Piper, Annie's, Aztec Diamond, and Arion. (Loooove the look of the AD leggings!)