You'll see Java EE tracks listed here (Enterprise Java), SE tracks listed here (Standard Edition) and ME tracks as well (Micro Edition). Oracle has various certifications on each of these topics. Oracle also lists their middleware server certification for things like WebLogic Server and Oracle Application Server here too. CodeRanch can help you out with all of these certifications, but the cowfolk here are far and away better at helping you with the Java focussed stuff.
Java 7 Certification Perhaps?
As far as the versions of five six and seven go, that's just the version of the JDK or technology that the exams will be testing you on. The Java 7 certifications are just being released. . OCAJP (Associate Exam) just finished its BETA testing, and the OCPJP exam hasn't started the BETA testing phase yet. You can find out more about OCAJP here:
With Java 7, the Associate exam is a prerequisite to getting the Programmer exam. With prior versions, you don't need the Associate designation to write the Programmer exam, so many people will be taking the OCPJP 5 and OCPJP 6 exams to get the Programmer designation in one shot, rather than having to write two exams.
Java Certification Exams from Oracle (Links go to Oracle's Exam Objectives Page)
As far as degrees of difficulty and how coveted the designations are, I'd rank them in this order:
So, if you have more questions about a specific certification, ask them in one of those forums and you'll get a whole whack of new information.
Warning: Blatant Unabashed Advertising Ahead!
Oh, one other thing. I joked about going to my page for more information about certification. I've been doing some work on an OCAJP Certification Guide for Java 7. I know it always looks bad when I spam a message thread with a bunch of links that point back to my website, so I created a page over in "Blatant Advertising" on CodeRanch that points to some of the content I've written. If you're interested in the Java 7 track of Java Certification, check it out: