Microsoft has released four new themes for Windows 7 and they are now available for download. The 2 themepacks are Diffusion theme and Galapagos theme.
Diffusion theme: Diffusion creates mysterious and beautiful abstract designs in this free Windows 7 desktop theme.
Galapagos theme: Make a natural selection and bring the unique species of the Galápagos Islands to your Windows 7 desktop with this free theme featuring photographs by Ryan Good.
You can also extract the wallpapers of any themepack and use them separately. Go here to learn how to make a Windows 7 themepack.
Do note that Windows 7 themes can only be used in Windows 7 Home Premium, Professional, Enterprise, or Ultimate editions.