I'm sure this is old hat to many of you, but I recently found a thread on boardgamegeek about mapping a sphere with hexes. Post 11 is the real meat of it.
Apparently you use an icosahedron as the base, then divide each triangular face into hexes, dymaxion map style. The points where the three faces meet? They're always going to be pentagons, although that might come in handy if you want particular nodes of power at certain places in the game world.
Of course, no mention of such a project in our circles would be complete without a suitable link to the Tao of D&D (just for the passing few who haven't yet stood stunned at the sight of a man gradually hexmaking an entire fantasy Earth, and then using those maps to model pre-modern systems of trade on a planetary scale).
Related, but less likely to be of interest to anyone other than me. Awww, what a cute little hex map of England. Anyone know how I can blow that up to a useful size without it pixelating horribly?