For me personally, I would define a "low-poo" as a gentle or moisturizing shampoo rather than strictly as a "sulfate-free" shampoo. There are surfactants that are just as harsh as (or more harsh than) sulfates in many so called sulfate-free shampoos. It also depends on the formulas. Often sulfate-free shampoos use greater quantities of milder surfactants which makes them more drying than a gentle/moisturizing shampoo that happens to contain a sulfate. (And Sodium Laureth--rather than Lauryl--is a relatively mild sulfate.)
Nexxus Therappe is a wonderfully gentle shampoo--I love it more than I ever thought I could love a "sulfate" shampoo. It's much kinder to my hair than countless sulfate-free shampoos I've tried (Giovanni, Avalon, Elucence, to name a few).
Two of my favorite sulfate-free shampoos are Mastey Traite and Terax Collagene. I usually CWC with them (coat the length of my hair in a light conditioner, shampoo the scalp, then rinse). My Honey Child cleansers are also nice once in a while.
2-something, modified CG, used to think my hair was straight until July 2007
Cleansing: V05 Passionfruit Smoothie (CO wash), Nexxus Therappe (gentle sulfate shampoo once in a while), Mastey Le Remouver (gentle clarifier once in a great while)
Conditioning: Robert Craig, John Masters Citrus & Neroli, Jessicurl WDT
Stylers: Oyin Shine and Define, Jason Lavender & Rosemary Curl Defining Cream, Herbal Essences Totally Twisted gel, Alagio Crazy Curl Balm