Option 1
http://jquery.malsup.com/corner/
Option 2
http://code.google.com/p/curved-corner/downloads/detail?name=border-radius-demo.zip
Option 3
Option 4
http://www.netzgesta.de/corner/
Option 5
EDIT:
Option 6
Option 1
http://jquery.malsup.com/corner/
Option 2
http://code.google.com/p/curved-corner/downloads/detail?name=border-radius-demo.zip
Option 3
Option 4
http://www.netzgesta.de/corner/
Option 5
EDIT:
Option 6