Google webmaster tools are now supporting the change of the domain name. If you are planning to change your existing website to a new domain name, this will be very helpful for you.
1. Move your old site to the new domain
2. Add a 301 redirect on the new site to the new website
3. Add your new website to Webmaster account (same webmaster account which you used with old website)
Read more from Google
[Via Blogs DNA]