I posted earlier about a.placebetween.us, a site that lets you enter two addresses, then finds a business of a specified type located about halfway between those locations as a convenient meeting place. GoogleMapsMania posts about a similar site called Mezzoman that does essentially the same thing. It’s a bit more convenient to use in entering the addresses compared to a.placebetween.us, but has a smaller map window with less flexible map controls (i.e. no zoom slider, just Zoom In/Out buttons). The initial drop-down business type selector is limited, but you can enter the business type of your choice in the Google Search box that appears after you click the “Mezzoman Go!” button.
Edited 6/13/07 to fix mistake pointed out in comments (thanks, Moawall!).