The AP or Advanced Placement courses are generally accepted as the equivalent of first year college courses. Completing an AP course successfully shows a college that you are ready for college level work. Most universities will give you credit for your AP courses provided that you score 4 or above on a 1-5 scale in the AP exam. Each institution sets its own standards, so the benchmark will vary. Check with your admissions office for details.
The IB or International Baccalaureate program offers high school matriculation credentials which are recognized world-wide. The impetus behind the IB movement has been the desire to create a set of universally recognized curriculum and assessment standards.
I'll get myself in hot water with both camps, but as far as I am concerned the AP is standard coursework on steroids, whereas the IB is a complete curriculum transformation. For a detailed description of both programs click here.