I think comptia.org has information on Linux +...I'd take this first.
LPIC is a good vendor-neutral test to take...I'd take this next.
RHCT information I think can be found on www.redhat.com/training
RHCT is all hands-on...be really comfy with what you're doing before taking the test. If you or your employer has the money, take the 4 day class before taking the test (RH 133). Also, studying the installation guide, sysadmin guide, and reference guides on www.redhat.com/docs
will help you out tremendously before taking the class.