Growing up we always bleached the beejeebers out of whites, and then added in a little blueing, which counteracts the yellow/grey tinge that all whites are known for. (We did the same for white socks/markings on the horses, as well, before shows... the blueing that is).
http://www.mrsstewart.com/ is the blueing we always used at home and in the barn. The website is, well, terrible. But the product is fantastic.