Contact customer service - many times by chatting with a customer service representative they will give you extra discounts to complete your purchase.
Use reward programs - check out such products as Swagbucks and Shopkick, these companies will give you special discounts and gifts for filling out surveys and shopping around.
Free Shipping - always look for free shipping coupon codes or for the minimum free shipping amounts to score this discount.
Use multiple email addresses - sign up for stores email lists using a couple different email accounts. Stores will offer single use coupon codes, combine these single use coupon codes from multiple email accounts to maximize savings.
Request price drop refund - some companies will give you a refund for the difference in price if the product you purchased drops in price.