From asp.net 1.0 to ASP.NET 3.5 asp.net having validation controls like required field validator,Compare field validation, Range Validator,Validation Summary, Regular Expression Validator, Custom Validator.
This control can be use very efficiently without writing much of javascript and other code.
I have found a great link which describes each and every aspect of validation control from asp.net 1.0.
Here is the link for that article..
http://msdn2.microsoft.com/en-us/library/aa479045.aspx