Lookup Field

Lookup Field

I am new to using JQuery. Is there a plugin/widget or something which would help me create the following:

I have a form field which holds a key value to another table. The user wants to be able to type key values into the field, but they also sometimes want to do a lookup and select one of the child table rows and have the key populated to the form field. I was thinking to have just a basic form field with a little "lookup" icon next to it. Is there a widget for this in JQuery? Some other slick way to accomplish it? Thanks!