I think i have a new favorite PrC.

[atemu1234]

Elder Druid from Dragon Magazine #286.

Any good builds for it?

[Biffoniacus_Furiou]

It's 3.0, but definitely still usable. Elder Druid Blade doesn't quite work the way it did, but you can still overcome DR/Epic with a 6th+ level spell slot. One thing to note about this class is that it does not need to use Druid as a base, and given its skill prerequisites that's actually one of the worse choices for entry.

I would probably use (Cloistered) Cleric, Wizard, or Archivist (http://archive.wizards.com/default.asp?x=dnd/ex/20051007a&page=3) to qualify. You need Knowledge: Arcana 10 ranks, among other prerequisites, so you can't start taking it until your 8th level. That means you can't start using Druid Sleep until you're 14th level, but any aging penalties you've gained prior to this should go away given its wording, "Provided the Elder Druid continues hibernating on a regular basis, he will no longer suffer the penalties of aging..."

For a full build that uses all ten levels, I would definitely include a single level of Binder to bind Naberius for Fast Ability Healing 1, and make the character an Elan (http://www.d20srd.org/srd/psionic/psionicRaces.htm#elans) which will never die of old age. This basically gives you unlimited spells/day, and you can even use Faerie Mysteries Initiate to avoid hp loss from the Con damage.

Overall it's a very unique and fun-looking class, but most of its strongest benefits (Druid Sleep) either won't come into play or will actually hinder the party in most games, since characters seldom die of old age, unless you're 17th+ level and can make use of Immolate Body.