The main intent I have for this thread is to allow us to share notes about cool PrCs we've found for D&D (and other games too, I guess) on the web or elsewhere. As to the one that got me excited enough to post this...
I downloaded the new web supplement on Wizard's site for Complete Divine, and found a Moon Guardian PrC there that looks really cool. I've always disliked the Monster Manual rules for Lycanthropes that played hackey-sack with your alignment. (as playing a werewolf would be really cool, but switching to Chaotic Evil (usually) sucks)
This PrC, however, allows you to be a werewolf without changing alignment. I also like the fact that it takes class levels to do so, since spending effort on mastering the beast within is kudos for roleplaying material. Very cool.
The doc is found here:
http://www.wizards.com/default.asp?x=dnd/we/20040522aI have reservations about the requirements (should only lvl 5+ divine casters be able to pray for deliverance from alignment change and be heard?) but the class creators also put in notes that almost encourage the DM to modify the reqs to whatever is necessary.
My take on handling the situation as a DM? First, make the PC a werewolf, full out. Start stripping class levels to make room for Werewolf HD and level adjustments (there should be a penalty for this, after all, but be careful not to tick off the player) and use Savage progression material if they don't have enough levels to manage that or aren't willing to sacrifice them. The requirements for the Moon Guardian should be entirely based on roleplaying, in my opinion. Let them struggle with the lycanthropy for a little while, and if they still haven't succumbed to the beast on their next level up, let them move into Moon Guardian.
Once there, if they have divine spellcasting levels already, great. The class works. If not, I'd count the even-level caster level increases as Druid spellcaster levels, as that works best with the theme. (Unless, of course they have a nature god for a patron diety, and then they could take Cleric spellcaster levels.)
Oh, and Knowledge(nature), possibly even Knowledge(Dungeoneering) should be on the class list. It doesn't feel quite like a perfectly-made PrC, but on the whole, I think it's very cool.