Forever 21+ - Young. Hip, and Trendy! Forever 21 + has recently (within the last 5 years or so) launched their PS branch. Everything is quite affordable, especially when on sale, but the quality of the material and how pieces are designed often suffers.
Lola Getts - an activewear brand that knows how to create quality products. I have a pair of the "Perfect Legging" which is great for any workout and has the right amount of fabric to keep your privates private during downward dog.
The Plus Bus - a second hand boutique, in LA, started by stylist Marcy Guevara and Jen Wilder. The Plus Bus is the perfect place to Buy. Swap. Sell.
Brands I hear people love, but I have not tried yet:
Igigi (recently relaunched, but seems to only be a variety of wrap dresses)
Did I miss any? Let me know in the comments where YOU love to shop?