RadAjax for ASP.NET AJAX
Contents
RadControls for ASP.NET AJAX

In order to assign different client-events to different ajaxified controls you can use the following approach:

CopyASPX
<telerik:RadAjaxManager ID="RadAjaxManager1" runat="server">
    <AjaxSettings>
        <telerik:AjaxSetting AjaxControlID="Button1">
            <UpdatedControls>
                <telerik:AjaxUpdatedControl ControlID="Label1" />
            </UpdatedControls>
        </telerik:AjaxSetting>
        <telerik:AjaxSetting AjaxControlID="DropDownList1">
            <UpdatedControls>
                <telerik:AjaxUpdatedControl ControlID="Label1" />
            </UpdatedControls>
        </telerik:AjaxSetting>
    </AjaxSettings>
    <ClientEvents OnRequestStart="Start" OnResponseEnd="End" />
</telerik:RadAjaxManager>
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />
<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">
    <asp:ListItem>111</asp:ListItem>
    <asp:ListItem>222</asp:ListItem>
</asp:DropDownList>
CopyJavaScript
<telerik:RadCodeBlock ID="RadCodeBlock1" runat="server">
    <script type="text/javascript">

        function Start(sender, arguments) {
            if (arguments.EventTarget == "<%= Button1.UniqueID %>") {
                alert("StartButton");
            }
            if (arguments.EventTarget == "<%= DropDownList1.UniqueID %>") {
                alert("StartDropdown");
            }
        }
        function End(sender, arguments) {
            if (arguments.EventTarget == "<%= Button1.UniqueID %>") {
                alert("EndButton");
            } if (arguments.EventTarget == "<%= DropDownList1.UniqueID %>") {
                alert("EndDropdown");
            }
        }
    </script>
</telerik:RadCodeBlock>

This way the DropDownList and the Button will have different client-events although using the same RadAjaxManager or RadAjaxPanel.