I think Astanga yoga (if you have access) is better than Pilates because as it was already stated, Pilates relies heavily on holding poses while lying on the ground and it does get boring. It's also been proven that the type of stretching can be harmful to people who don't already have a lot of muscle mobility because it involes pulsing during certain moves. That's usually the toughest part for men as their hamstrings are usually really tight and hamstrings are the bases for many moves.
Astanga yoga is a killer workout too, when I had my 6pack, that was how I got it.
You can buy DVD's for it or just find some postures on the 'net and practice them in succession.
I always found taking part in a class was the best motivation (but I'm biased cuz I used to teach yoga)
Best of luck