Since Q2 2010 all new functionalities are listed in the control's Release Notes posted here.

• VS 2010/.NET 4 RTM support
• Spaces after an autocomplete separator are ignored when matching Items (MarkFirstMatch=True)
• Added Localization property
• Bug-fixes

• jQuery updated to version 1.4.2
• Automatic Load on Demand
• New property: Label
• Added javascript intellisense under VS 2008/ VS 2010
• RadComboBox now escapes single quotes before doing a Load On Demand request
• Bug-fixes

• Bug-fixes

• New Skin - Windows7
• Bug-fixes

• New Skin - Sitefinity.
• Performance optimizations on the server
• Support for Visual Studio 2010 Beta 2
• Bug-fixes

• Bug-fixes

• Bug-fixes

• Full support for Google Chrome v.2
• Compatibility with Visual Studio 2010 Beta 1
• New common skin: Simple
• Added support to render properly in callback / MVC / webservice scenarios
• Bug-fixes

• Full support for Internet Explorer 8
• List of the fixed problems can be found here

• Animations are using the jQuery library now
• Added new property UseHttpGet to the WebServiceSettings properties. By default its value is False.

• New event: OnClientItemDataBound. Fires for each item that is created during Web Service Load on Demand.
• New method: clearCache - clears the cache when EnableItemCaching is enabled.
• Full list of the fixes can be found here.

• There are no new features. List of the fixed problems can be found here.

• MaxHeight property added to allow the height of the dropdown list to vary depending on the number of items.
• AccessibilityMode property added. If it is set to true noscript tag containing select html element will be rendered. This select will be displayed instead of RadComboBox if the javascript is disabled.
• Better performance - lazy initialized items. They are initialized when the dropdown is opened or they are accessed for the first time.
• Added new server side methods FindItemByText, FindItemByValue, FindItemIndexByText, FindItemIndexByValue which have a second argument ignoreCase which indicates whether the comparison is case-sensitive (true) or case-insensitive (false).
• Added a new server side method FindItem which has one argument match of type Predicate Generic Delegate. This method can be used to find an Item by some custom criteria.
• Added protected virtual methods for server-side events – OnItemDataBound, OnTextChanged, OnSelectedIndexChanged.
• Support for server-side expressions (<%= %>) in the ItemTemplate.

• OnClientTextChange client-side event

• Added design time support for HeaderTemplate and FooterTemplate
• Filtering functionality now works with AutoCompleteSeparator

• Filtering
• Sorting
• Adding images to items
• ClientChanges property added to RadComboBox class. Now client-side changes are available on the server side after postback.
• EnableTextSelection property added to RadComboBox class.
• ChangeTextOnKeyBoardNavigation property added to RadComboBox class. If set to False, the combobox will not change its text in the input area when you scroll down the items with the keyboard.
• Added get_visible, set_visible, show, hide, get_imageUrl, set_imageUrl, get_disabledImageUrl, set_disabledImageUrl and findControl client-side methods of RadComboBoxItem object.
• Added get_visibleItems, setAllItemsVisible, get_changeText, set_changeText, get_enableTextSelection and set_enableTextSelection client-side methods of RadComboBox object.
• Gray skin has been added. The Mac skin has been removed from the Telerik.Web.UI assembly. More information on Q2 Skinning is available here.

• Footer templates
• Load-on-demand items caching
• OnClientDropDownOpened client-side event
• OnClientDropDownClosed client-side event
• When creating items with the Item Builder, if you don not set the Value of the item - it will automatically become equal to the Text property.
• attachDropDown client-side method. Use it in the scenario described here: Ajaxified control in ItemTemplate does a full postback

• IsSeparator property
• Additional feature to KeyBoard navigation: If RadComboBox is in “readonly” mode (AllowCustomText, EnableLoadOnDemand and MarkFirstMatch properties are set to false), keyboard can be used to navigate items, e.g. pressing the "c" keyboard button will iterate through all items which text starts with "c".

• Added get_domEvent to the event arguments of all client events
• EmptyMessage property
• Added Value property to the event arguments of the SelectedIndexChanged server-side event

Other Resources