I've always sprinkled baby powder on my second (and the occasional third day- eek) hair to prolong having to wash it. And then I met Oscar Blandi's Pronto "Dry" Shampoo and fell in love. I consistently use this product on my roots. It gives my flat ironed dry ends an extra day and it's a lifesaver when I'm just feeling too darn lazy. It has a light lemony scent and you don't need to use a lot to get results. For best results I find that I just need to sprinkle a little on my palms then rub it into my roots or wherever I need it.
Note: I've tried the nozzle spray version and the power is far superior- the nozzle clogs way too easily.