There are a bunch of resources that can be had. I suggest that if you are not an experienced admin, avoid the "cram" book, as they assume you already have a fair amount of know-how. Take a look at:
When I was teaching prep courses, I used the objectives for the RHCE from Redhat:
and just covered the objective according to the needs of my students.
Bottom line, as far as I can tell, is that there is not one comprehensive "best text" for the RHCE. Some books have strong points, some have weak points. I hope some of the RHCE's in the forum will chime in with their experiences...
Good luck! Certification raises the level for all of us. Like what's her name said, "it's a good thing."