Sun offers a track to get you Sun certified. Take the classes then take a Prometric test at a local testing center.

There is Usenix/Sage and Lopsa that provides a generic admin class but it's cross platform. Unix and Windows last time I looked (it's been a while though).

HP offers on-line classes with virtual servers for you to configure (I'm scheduled to take a VCS/ServiceGuard class soon).

IBM has their RedBooks which have quite a few good books.

Carl