AJAX AutoComplete Feature Implementation Example

1.       Add AJAXControltoolkit dll in your web site reference
2.       Drag n drop script manager on the top of the page (if already included inmaster page then no need)
3.     Place folowing html in your html page

<ajaxToolkit:AutoCompleteExtender ID="AutoCompletePeople" runat="server" TargetControlID="txtUsers " 

DelimiterCharacters=","  MinimumPrefixLength="1" ServicePath="NewQuestion.aspx"

ServiceMethod="GetUsersList" UseContextKey="True"

EnableCaching="true"

CompletionSetCount="5"

CompletionInterval="1000"

BehaviorID="autoCompleteBehavior1">


4.      Write following code in aspx.cs class file

#region AutoComplete Users

        //Specify this method as ServiceMethod for Company Completion List

        [System.Web.Services.WebMethod]

        public static string[] GetUsersList(string prefixText, int count)

        {

            string[] result = selectUsers(prefixText);// this method returns all the users

            return result;

        }

        #endregion  AutoComplete Users END

Here is the link for AJAX  Auto complete features  and more

http://www.asp.net/ajax/ajaxcontroltoolkit/Samples/AutoComplete/AutoComplete.aspx