Cornerfly is a very simple customization app that rounds the corners on your Android screen to give it a more elegant touch. In the setup options you can also customize which apps you want to see rounded corners on (by default all of them). Other configuration options let you adjust the size of the rounding and color of the corner edges, which is preset as black.
Cornerfly is a really simple app ... but it offers really great results. The look of the screen with its corners rounded is so elegant that you probably wont wan't to go back to boring old square corners once you try it out.