I don't use anything fancy but sometimes I just put a little baby powder in my hair if its dirty. It soaks up any grease & smells fresh... That is essentially what all the other instant shampoos are anyways. :)
I'm not sure of the availability of this but I use Kevin Murphy Fresh Hair. It's an Aussie line and the Fresh Hair smells like anise so that when I'm lazy, I don't smell icky.
(OK so I also wear this because it doesn't really compete with my Lolita Lempicka)
I WOULD use baby powder except my hair is naturally jet black and I'm not a careful enough applicator of anything so I would look a bit Cruella De Vil-esque after using the BP.