You might keep an eye on the PowerMonkey. It's $110 now but I bought it a month or two ago with an $80 rebate (which they did indeed honor), and maybe that rebate will show up again. I haven't used the solar part yet (I live in Seattle, and sunshine here has been as common as Bigfoot), but the rest of the thing works very nicely and gives me hope that the solar charger will, too. Also, the PowerMonkey's overall approach (having the solar trickle into a battery that can then be attached to the Nokia once it's all charged) may circumvent the problems that jolouis mentioned above.

Here it is, at the moment without benefit of rebate: http://tinyurl.com/4xqn9z