You might have to pay a bit more for shampoos that are naturally derived, but you won't be sorry. Also, natural conditioners like jojoba oil, coconut oil, rosehip oil or even extra virgin olive oil are excellent softeners and defrizzers.
There is a new line from Sammy's called SammyPure that has no SLS in it. They run about $5 a bottle and can be found at Target and Rite Aid. I have not tried it yet, I am waiting for my shampoo to run out! I sometimes have found taht natural shampoos like the bars from Lush and stuff from the health food stores dry my hair out. I like Pureology but $20 a bottle is out of my budget at times!
I really love the Lush conditioners but they are pretty expensive and I have to use heaps because my hair is long and very thick. The American Dream one is to die for! I've never had softer silkier hair. I've been on a real natural kick with cosmetics lately so I might just try Lush again. I bought a natural soap (derived from things like coconuts olive oil etc) from the health food store, but it's just not the same as regular shampoo.