What Shampoo/Conditioner should I use?

I have naturally straight, thin hair. I get it colored every few months, and currently am using Garnier Fructis Color Shield Shampoo and Conditioner. Lately I've been realizing that it isn't giving me the same effect it was when I first started using it, and this normally happens with shampoo/conditioners after I have been using them for a while. What is a good colored hair shampoo/conditioner that isn't too pricey?