I have not looked through the materials in depth yet, but they seem to be inferior to the study books that are commercially available. However, there are some practice exams that might help and the best thing is that the following exams are greatly discounted (supposedly $300 exams are lowered to $60 - a much more reasonable price):
Sun Certified Java Associate (SCJA)
Sun Certified Java Programmer (SCJP)
Sun Certified System Administrator (SCSA)
Sun Certified Network Administrator (SCNA)
Sun Certified Web Component Developer (SCWCD)
Sun Certified Solaris Associate (SCSAS)
Although I wish there would be a greater offering (I'm doing my SCJD right now) I'm still happy that I can take these certs at an affordable price. I'm sure other students would agree.