My favorite online clothing store hands down is ASOS. River Island would be tied with ASOS, but you can't beat ASOS' shipping compared to River Island's
I shop online at department stores and Kohls to get a look and see if the outfits I want to try on are in store, DSW for shoes, and swimsuitsforall for my swimsuits.
It's not super high quality but with a husband and child that wear out clothes way too quickly, I love Kohl's! They always have sales and the clothes last just as long for us as higher brand names. Plus they are always giving away Kohls Cash and having amazing deals!