For shampoo and conditioner that are truly superior, I recommend Redken.

The 33.8 oz (1 liter) bottles are the best value, shampoo retailing for $22, and conditioner for $29.  However, Ulta has "buy 1, get 1 free" offers on the Redken line several times a year.  My local Hair Cuttery sells two 1-liter bottles for $30 as pictured above.  So, apparently, the giant bottles of Redken conditioner are really only worth $15.  Don't pay more.  If you prefer the smaller bottles, try to get a deal close to $0.44/oz for conditioner, $0.32 for shampoo. 

Those with Ulta membership cards (it's free and not a store credit card) can also apply the $3.50-off coupons included in their monthly mailer for even cheaper Redken!