I'm a big believer in finding things on sale; you can often find better quality items for an affordable price, and for most things, it doesn't really matter that they are a few seasons old. Here are some of my favourite retailers for discounted fashion:

Barney's Warehouse (from Barneys)

Saks Off 5th (from Saks 5th Avenue)

Nordstrom Rack (from Nordstrom)

The Outnet (from Net-A-Porter)

Tk Maxx (look out for their premium brands in Contemporary Clothing)

My-theresa (they have a Sale section that's always available)

Matchesfashion (their Sale section is always online)

Designer Shoe Warehouse (has great deals on luxury brands like Tod's, Prada, Sergio Rossi, Jimmy Choo..)

Yoox (a very extensive - almost overwhelming - selection of clothing, both at retail and on sale. Brands like Rick Owens, Prada, Jil Sander, Isabel Marant...they have everything. Lots of italian shoe-wear brands that are really nice)

Vestiaire Collective (my go-to for second hand clothing. You can trust that the quality of their items is the best in Europe)