A while ago I posted a table relating kite size to body weight and wind speed for kiteboarding. It starting getting a lot of hits, so I decided to go ahead and soup it up as an entirely interactive kiteboarding calculator, modeled after my windsurfing calculator spreadsheet. It has two pages- one for kites and one for boards, which you can switch between by clicking the "kitesize" and "boardsize" tabs at the bottom. As with any effort to apply simple math to a complicated and subjective thing, it ain't perfect, but it ought to help give less experienced kiters a rough idea about what kind of gear they need.
If you can't view the embedded version, you can download the file here.