Contact customer service - many times by chatting with a customer service representative they will give you extra discounts to complete your purchase.
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.
Set up discount email - to clean things up, set up an email specifically for collecting coupons and discounts without cluttering your personal email.
Enter multiple coupon codes - combine multiple coupon codes at checkout to score the biggest savings. Also referred to as stackable coupons; combine a sitewide coupon with a free shipping code.