Free CLEP Biology
http://www.collegeplus.org/clep/clep-biology
The CLEP Biology covers course material taught in introduction to biology college courses. The exam emphasizes molecular and cell biology, organisms, and concepts like ecology, evolution, and human behavior.
http://www.testprepreview.com/biology-questions.htm
Selection of 10 questions on CLEP Biology. This free CLEP test comes complete with answer key.
http://www.speedyprep.com/clep-practice-test/biology
The 15 questions on this practice test are similar to those on the CLEP Biology test. The answers come with useful feedback. Best of all the questions are updated each day so you can test yourself on a regular basis. A great way to reinforce learning.
http://www.cleptestreview.com/clep-biology-practice-test
On this site CLEP Biology is broken down in to several subject areas and each subject has its own quiz (monthly cost). At the end there is a timed one hour exam (free) that will be a useful test of your readiness for the real thing.