Well, the crowning champion of pelvic floor strengthening exercises is the Kegel, especially for women. For more info on what Kegel exercises are, what muscles are employed and how to perform them, click here.
I've included a video with a couple of exercises that I think are useful. They not only target the pelvic floor, but the transverse abdominis (TVA) as well.
The transversus abdominis muscle, also known as the transverse abdominus, transversalis muscle and transverse abdominal muscle, is a muscle layer of the anterior and lateral abdominal wall which is deep to (layered below) the internal oblique muscle. It is thought to be a significant component of the core.
In the video I use a hand gesture to indicate the TVA going across the pelvis, like a lap belt. The TVA doesn't actually run in this manner. I guess I've always thought of it as kind of a strapping down muscle when activated. Because the TVA runs under other muscles of the abdomen it fires everything up when engaged. So ignore my hand gesture, or use it as a mental reminder of activating the TVA.
I hope you find these useful.
Enjoy the dance that is life!