What is a good online discount clothing store?

http://www.asos.com

http://www.girlprops.com

Oldnavy.com or amazon.com. They are not the cheapest, but are reliable.
During the holiday event or season clearance, they will offer some great discount for clothing items. Oldnavy sometimes will release 70% off discount.

For amazon.com, you know it is a well-know brand and also many many sellers including macy levis .. are selling products on amazon.com. The good part is that amazon ALWAYS has some great discount offers. Such as 50% levis, 70% macy discount, you can save a lot of money if you catch up these items.

For more clothing offers on amazon.com, you can check their apparel page http://www.amazon.com/apparel-accessories-men-women-kids/b/ref=sa_menu_apr9?ie=UTF8&node=1036592&pf_rd_p=328655101&pf_rd_s=left-nav-1&pf_rd_t=101&pf_rd_i=507846&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0K2YSW9ZZNJ9MTYF95XH
or this site: http://www.tophotdeal.com/amazon-discount-finder/category/apparel-accessories/

Hope that helps.
Good luck.