We picked up an Evolve RoadRunner showerhead at Costco last weekend ($28). I love this product! You turn it on and it allows the cold water to run until the hot water starts to flow. Then it automatically shuts off the water flow until you pull the cord. Obviously this saves on energy costs by not running the hot water unnecessarily. But I also love that I can tell exactly when the shower is ready by listening for the water to stop.
I was a little skeptical about how well it would work. But after a week of use, I'm extremely satisfied with it. The ShowerStart feature works flawlessly. And it has a very strong pressure even though it's a low-flow showerhead. Highly recommended.