Pilates certification programs vary a lot in their structure. Most are oriented toward the working adult and make use of intensive sessions with breaks in between. How those sessions are structured over time is different for each program so it is worth looking around to find a program that fits your needs.

Another important consideration at the teacher training level is whether or not you want to pursue classical or contemporary training. These terms are often used to distinguish between traditional training that adheres strictly to what Joseph Pilates taught (classical); or training that incorporates new techniques and developments in exercise science (contemporary). Excellent training for both styles is available.

Body Harmonics
Body Control
Balanced Body University
BASI Pilates
Core Pilates, NY
Peak Pilates
Physical Mind Institute
Polestar Pilates
Power Pilates
Power Pilates teaches classical pilates, which is very close to the original exericises that Joseph Pilates created and taught in his New York City studio in the early 1900's. Power Pilates has studios throughout the United States, which is great because you can look up a Power Pilates studio anytime you travel to a different city. You can expect the teaching styles and exercises to be taught in the same consistant way in every Power Pilates studio.
Romana's Pilates
Romana Kryzanowska was Jo''s student and protege'. She was asked by Joe to carry on his legacy, which she has proudly done. Now in her 80's, Romana still does pilates herself and runs the certification program with her daughter and granddaughter, as well other instructors they have certified. This type of pilates is called "authentic", "classical", "old-school", etc. Some details about this type of instruction are strongly debated by instructors who do not teach from this approach. For example, neutral pelvis is not taught, instead, the low back is pressed down into the mat.
Ron Fletcher Program
Stott Pilates
Ellie Herman Pilates
Ellie Herman Pilates teaches many of the classical exercises, but with a lot of variations as well. In general, this style approaches pilates from a more dancerly perspective and can be a fun way of adding new and creative exercises to your pilates routine.
Kelly Kane Pilates
A teacher from Kelly Kane will have strong knowledge of anatomy and understanding of injuries and will move you through the exercises with ease and precision, slowly strengthening your body back to health.
Body Tonic
Any teacher from this certification is an awesome, thoughtful, well-educated instructor, with a classical approach and knowledge of anatomy.
Core Dynamics
Core Dynamics is a studio that teaches pilates based on Eve Gentry's style of pilates. Eve was a dancer and student of Joseph Pilates who had a gentle, theraputic approach to her teaching style. Look for any instructor who mentioned that they're certified under Core Dynamics or who mentions that they have an Eve Gentry approach to pilates.
Winsor Pilates
Founded by Mari Winsor, is one of the more well-known styles of Pilates, as Mari Winsor launched a large-scale infomercial business based on her success with celebrity clients. This is the "as seen on TV" site, so it's loud, flashy, and certainly trying to sell stuff, but many people swear by the products offered.
Dianne Miller
The Gyrotonic
Is a machine that offers complete range of motion and improves core strength, expands the spine, and puts the body in equilibrium. Although not technically Pilates, Pilates principles are applied on a Gyrotonic machine, and it may be used as a supplement to Pilates study.