Our application is developed using Java based Technologies like Servelets and JSP's and it is running on Weblogic.
We would like do automation for functionality and regression testing of it to test on different OS's and Browsers.

Please sugust me about the best Tool for automation which really saves time. We need to run the same scripts in all the browsers as well as OS's without any problems and modefications.

Thanks in Advance
Ramana

You will have a very hard time making test scripts that can run on many browser versions.

You should probably look into something like SilkTest that will simulate actual keystrokes and mouse movements and can validate that screens and dialogs contaion the expected elements.
However, since screen layouts, button placements and so on will vary a lot between browsers (not to mention OS's), you will probably be able to run the same tests on all browsers - there is just no way that the same script can test a Windows CE Internet Explorer and a Lynx browser runing under Unix.

I would instead recommend using two types of testing: One set that sends http requests and examines the html returned to ensure that it contains what you want. This can test a large number of scenarios.

A second test set can test a limited number of scenarios to ensure that styleshhets, colors, layout etc works as expected on a number of different browsers.

i think rational Team test, Silk, Load Runner etc are the available tools for Functioanlity testing for Web applications