Well, the dolphin kick, to me anyway, is a huge thing. As soon as I did it, I felt I was going much much faster. Here is a video of Kitajima, a Japanese Olympian who could have been disqualified for doing this kick, demonstrating the proper dolphin kick. I say proper even though it is illegal in competition.
http://www.swim.ee/videos/breast/DQ-legkicks-after-start.mpg
As you start the arm-pull, dip your head slightly, the raise it back to streamline position, dont just bob the head though, let it start a ripple that travels along your body. While it travels back, increase the amplitude. As it gets to your legs, bend your knees slightly and then finish it off with nice, powerful down beat. The video really helps, watch it closely, there are other little things to see there too, possibly a little improvement on the arm pull. Hope this helps!
Ike
http://www.swim.ee/videos/breast/DQ-legkicks-after-start.mpg
As you start the arm-pull, dip your head slightly, the raise it back to streamline position, dont just bob the head though, let it start a ripple that travels along your body. While it travels back, increase the amplitude. As it gets to your legs, bend your knees slightly and then finish it off with nice, powerful down beat. The video really helps, watch it closely, there are other little things to see there too, possibly a little improvement on the arm pull. Hope this helps!
Ike