Okay here's one for the deep-pocketed Greens out there (or maybe somebody on assignment to the middle of nowhere). QuickTek is offering a line of solar chargers for the MacBook Air called the Apple Juicz
. There are three models of increasing size: 18 watt, 27 watt, and 55 watt. They recharge a MacBook Air in 14, 8, and 5 hours respectively, but all this solar powered goodness doesn't come cheap at $500, $600, and $1000. On the bright side though, they'll throw in a "very cool Element carry bag" for free, which you'll need as the largest one unfolds to 60 x 42 inches.
In addition to the solar panels you'll also need a modified MagSafe power adapter. QuickerTek will upgrade yours for $25 or sell you one pre-modified for $100 (which includes car and airline adapters). They suggest that this would be the ultimate gift for a college student, but even as a geek prof I'd be tempted to take the lunch money of anybody I saw on the quad with 17 square feet of solar panel laid out on the grass. But maybe that's just me.