Don't disparage using a PIC (or other) microcontroller. It may take you a bit of time to learn, but it will be far cheaper than any other way of making (or, gasp, buying !) an MPPT solar charge controller, and you'll be able to use the experience for many other things.
If you want to go with a discrete buck converter (one of Amanda'a suggestions) you could do that, too. The MPP is usually 80% (in voltage) of the open circuit voltage, and the open circuit varies slightly with insolation, but mostly it varies with cell temperature (which is a factor of mostly insolation and ambient temperature). While it is great to dynamically track the MPP, if you just adjust it seasonally, you'll be most of the way there. When you decide to, you could always upgrade this buck converter with a microcontroller (not to directly drive the PWM, just to give the feedback to the circuit).
If you have no programming experience and want to make it a little easier on yourself, you could get a picaxe for a bit more money than than a PIC or AVR ($10-15 vs. $2-5); it's got an onboard BASIC interpreter. If you're interested in doing such a thing, I would be willing to help (I'd prefer a PIC or AVR, though), just post to the board.
Dave