Take a look at Carparts4less, the web only sister of Eurocarparts, compare the prices between the two and 4less usually comes out cheaper.
Also take a look at Brakes International for their prices and others like Micks Garage on line. AutoDoc on line also wo rth a look but delivery takes longer from them and you may get stung for delivery on top of the parts prices.
Don't forget to use any discount codes these sites have on their home page and keep an eye out for their specials on brake parts that come up frequently.