Update .net textbox value on client side (js/jQuery)

Question

I have a textbox in html. After user select a value from the asp drilldownlist, i need to read data from the database and update textbox value on client side. I am not so keen to use Update Panel unless I have to. Also I would stay away from the web service. I have a feeling that I can do it with jQuery but after few days surfing the Internet I can't find a clear smart solution for it. I will be very grateful if someone can share "know how" with me! Many Thanks