Create CSS Rounded Corners by css or images

There are several good resources teach how to create rounded corners by css and images.

1. Google Rounded Corners Generator

http://groups-beta.google.com/groups/roundedcorners? c=999999&bc=white&w=4&h=4&a=tr

2. Spiffy Corners

http://www.spiffycorners.com/sc.php?sc=spiffy&bg=ffffff&fg=0a67e6

3. Cornershop

http://wigflip.com/cornershop/

They can generate css source code and images based on your demand. Really useful.