To me it depends where you pull your practice tests from, as well as the exam.
The sources I've used in the past were:
Comex books (good at reinforcing a chapter, but the questions are sometimes too easy)
free-clep-prep.com's practice tests (free, but needs registration; heard good reviews all around and helped me with Macroeconomics)
Peterson's (won't let me post link here for some reason; very hit or miss, as an example the Ethics in America's practice tests' latter halves can be skipped IMO)
5 Steps to a 5 books (AP prep books, I used specifically for both Economics exams, and were excellent in both teaching and testing the material)
REA practice exams (varies; gets too indepth at times)
Passbooks (
http://www.passbooks.com/dantes-subject-...s-dantes/; not a personal fan, as it's mostly just test questions and some are ridiculously specific, and the answers don't explain how)
The sentiment I've seen around here is that if you can do well enough on the practice exams, the actual exams are usually easier. That being said, some of the study materials I've seen/studied don't really reflect the actual exams at times; it was only with heavy reading/studying that I did as well as I did on the Ethics in America exam as well as Analyzing and Interpreting Literature.