Need help with Validations

I have problems when I validate a web control using the requiredFieldValidator. The validator catches the error and displays a message fine. But, when I try to do something like making a new selection in my dropdown box, my form does not post back. I added autopostback=true to the controls being validated and everything works fine. However, I don't like my form performing a postback everytime I take focus off the control being validated. I don't want to write my own javascript to validate since it is a lot of work. Is there a better way to validate without the postback when a control loses focus?

Please help,

James