I suffer from itchy scalp, so alternate shampoos all the time, as that helps. The one I would most hate to run out of is: Original Source Tea Tree and Mint Shower Gel - yes note it is the Shower Gel not shampoo.
I came across it when two bottles were delivered with my Tesco order, I hadn't ordered them and I wasn't charged. I tried to give them back to the delivery guy but he practically implored me to keep them . . . I think he was tired and at the end of both his shift and tether, and couldn't face the paperwork.
I found the shower gel too, um, invigorating for my nethers, but determined to use my freebie [tightarse emoticon] I used it as a shampoo, reasoning that a) it's all the same stuff anyway and b) if it had tea tree oil in it hopefully it would be soothing.
I found it the best stuff for my itchy scalp I have found for a long time.
They have since bought out a shampoo, but I prefer to stick to the shower gel as I know it works for me (and yes I know I just said it's all the same stuff
)
I also use the purple one, tea tree and lavender, which is OK but not as good, but smells fab.