I like the Giam begining mat workout and there is another called the Method. Both are for beginers and focus on form and breathing while teaching you the moves. The Giam one features two people working, one doing a modified version to help start getting ab muscles in shape.

I really loved the Giam Pilates for Weight Loss. It featured 3 different workout levels. Unfortunetly due to encoding problems the DVD won't play all the way through on some machines. If you are looking for VHS though, that won't be a concern and I heavily recomend looking into it.