This is a sample portlet with autocomplete-list implementation with AJAX request data from server side.
http://www.moisesbelda.com/campos-autocomplete-ajax-en-liferay-6-2/
Sources:
http://www.liferay.com/es/web/meera.success/blog/-/blogs/liferay-auto-complete-list-with-ajax
http://alloyui.com/api/files/yui3_src_autocomplete_js_autocomplete-list.js.html