I don't know how it is with you, but when I seem to be slogging along on a project and am in need of a quick knit, I usually turn to dishcloths.
They never take too long, the yarn costs only a bit and comes in such bright, cheerful colors. To top it off, the internet is full of free patterns so there is something new to try every time you get the urge.
This one was just a HOOT to knit. : )