Despite legibility problems, sometimes you just have to use teensy little text on a site. What you usually do is use 8-10 point Arial, Verdana or some other sans serif, but most typefaces begin to break down at these sizes.
One answer to the problem is a new set of characters called The 9-pixel Typeface. It invites anyone to help decide what actually works. Does a lowercase 'w' look best at 5 or 7 pixels' width? Well, let's have a vote!
The rules for the 9-pixel Typeface are simple. Characters must fit inside a 9x9 pixel square, have an x-height of 5 pixels (where it applies), and, of course, be as legible as possible.
Examples (point for larger version):
