Here are some I quickly mocked up for some popular websites you can easily find on the web:

This second one in particular, I originally copied the logo and header shape. However after introducing it to Photoshop I was able to make the curves consistent on the top and botton of the header and introduce new text.

The first header on the other hand was created from scratch. Using the pen tool and my mouse I was able to establish the curves exactly how I wanted them, as well as use them to shape the head of the keys. One of the clever things about photoshop is that when you use the pen tool, you can easily correct/modify the shape using the Direction Selection Tool and change the shape of the curves.

Now getting these curves to look smooth will take practice and a lot of zooming in to help smooth out the lines, but it is definitely worth the effort once you finally achieve the end result.

So give it a try and see how you get on.

Michelle