Lululemon makes excellent gear. I've had a number of pieces for many years and they have held up very well. It is expensive and I have no idea how long current versions will last.
I've recently made the switch to wearing designer medical scrubs for yoga (I'm of intermediate skill) and exercise. There has been a huge upgrade in the quality and types of scrubs out there (i.e. see women's scrubs review
) in recent years and they are fashionable, comfortable, highly durable and stretch well. You can get them through Amazon or only directly from the companies in some cases.
Athleta is another brand that looks promising but I have not given it a try. Does anyone have experience with that brand?