Last year in July we decided to buy Telerik Suite here for our team and I think it has been a wonderful decision. At the time, we started working on an highly data intensive application and we had to reduce postbacks using AJAX. I had used ASP.NET Ajax Control Toolkit before (like here) but I found it limited and you still have to do a lot of work around the toolkit controls to actually make them work in more complex scenarios. So we decided to give Telerik controls a go and it has been amazing !
We have used various controls from the Telerik Suite in our applications like RadAjaxPanel, RadEditor, RadToolTip, RadChart, RadGrid, RadInput, RadUpload, RadSplitter, RadWindow. All these controls are useful and not only provide an amazing UI but also reduce the development time considerably, still I have fallen in love with specially two controls RadAjaxPanel and RadToolTip.
Rad Ajax Panel is an enhanced version of UpdatePanel with a wonderful Client Side and Server Side object model to work with. So, just put an RadAjaxPanel around everything you want to Ajaxify.
<telerik:RadAjaxPanel ID="RadAjaxPanel1" runat="server" Height="100%" Width="100%" LoadingPanelID="RadAjaxLoadingPanel1" HorizontalAlign="left"></telerik:RadAjaxPanel>
RadToolTip is an amazing control and can be used in a range of scenarios specially for on-demand loading. You can actually fit a Web User Control in the tool tip and load it on demand on any event on the page. Some of the scenarios where we used the RadToolTip.
Data Validation (Since it can stick to any control on the page)
Dynamic Selection Menu (Loading On Demand User Control)
Dynamic Options (Loading On Demand User Control)