Currently it seems that kendoDropDown only supports select elements with options and not optgroups. Would like to see this widget support select elements with both optgroup and option elements.

New control ComboBox with CheckBoxes

Currently when you enter custom text (referred to as custom value) the control sets the text entered as both the TEXT and VALUE.

I suggest this should operate like the Telerik ASP.NET combobox which only binds custom entered text to TEXT and null as the VALUE.

This then allows you to differentiate between an item selected from the list and one entered.  When you call text() it would return the selected item text or custom text entered and value() would return the selected item data value or NULL if custom text.

There are a couple of things that are very common that I would like to add buttons for.  The first is for clearing the value and the second is a + for adding new items to the list.

The + button is an important one from a usability standpoint.  Quite often the combo/dropdown is populated from a list that is managed on a separate page.  It is too cumbersome to have to use stop entering and go to the admin page to add the new item and then come back to add whatever they were working on previously.

I know I could simply add a button beside the widget but this just doesn't look as nice as it being built in.

When using IE10/11, it natively supports the clearing of input element so essentially when hovering over a Kendo ComboBox with a selected value, this is the end result:

http://i1256.photobucket.com/albums/ii484/vobreshkov/KendoComboBox_IE.png?t=1376577876

I am constantly getting requests to have such way (or adding an extra menu item) to my combo boxes to allow users to click on something and clear the selection. Please consider extending similar functionality to the combo box that is available on all browsers.

The option to allow new items to be added to the list, as opposed to items exclusively in the datasource.

For example see this: http://jsbin.com/iXEtonO/4/edit, only built in

Check out this idea. It may help solve this issue and help with UI presentation.
http://feedback.kendoui.com/forums/127393-kendo-ui-feedback/suggestions/3767009-treeview-in-combobox

Admin edit: A Knowledge Base article that shows how you can achieve this: https://docs.telerik.com/kendo-ui/knowledge-base/disable-multiselect-items

A kendoDropDownList places an arrow to the right of the <select/> element, indicating it's a dropdown (.k-i-arrow-s). It would be cool if kendoMultISelect did the same thing. 
Clicking the <select/> element or the arrow should also toggle the visibility on the list items.

See http://stackoverflow.com/questions/31825788/kendo-multiselect-to-have-arrow-icon-and-behavior-to-close-on-click .

When bound to oData, the autocomplete contains filter should treat each WORD as a new "substringof"....or make a new odata advanced contains type\property.

This is more what users expect when searching...and the odata spec has it covered.

http://www.kendoui.com/forums/ui/autocomplete/odata-google-like-filter.aspx

The grid and autocomplete widgets really need no-data templates which display when the returned data is empty. The MVC controls were pretty good at this.

Fast and responsive UI rather then flaunt and animated. 

I have played for a while with the demo of the components.
What I noticed is that components with popup elements, such as ComboBox, DatePicker, TimePicker, ... have a small but visible delay, which becomes quite annoying with time.

Look at ComboBox demo, it seems there is some delay due to pre-configured animation effects on the control.  In slower browsers (take Firefox 6.0.2) the delay is obvious. 
The support for animation in general is a cool idea, but in most business applications it is not welcome by users who use application on a daily basis. 

Personaly, looking at the demo I am not sure if I can rely on kendoUI if my application designed for "do the job" rather then "enjoy UI".

I think it would be very nice if the demo has settings to disable all animations, to run it at full speed and demonstrate rich AND really responsive UI.

It would allow selected items(Tags) to be displayed as well as add new ones or select ones from an autocomplete dropdown.

I'd like to add separators between groups of items in a select / kendoDropDownList. Also known as a horizontal line or delimiter.
The same question was asked here by someone else: http://www.telerik.com/forums/separator-in-dropdownlist
The answer was that this is not supported.

The combobox currently doesn't react on the disabled-attribute for options. It should be possible to make single options visible but not selectable with this attribute as in original html-select:
http://www.w3schools.com/tags/tryit.asp?filename=tryhtml_option_disabled
I found no way to do this yet.

It will be very nice if the AutoComplete, DropDownList, ComboBox, and MultiSelect components have the floating label functionality like the TextBox widget 

Currently when a combo box is used on an edit form, when the combo box first loads, the value property it is bound to (e.g. an int id) is displayed as the text until the databound event fires, and the text value associated with that value can be loaded.  It gives the combo boxes an unprofessional look, as they briefly display a number until they are done loading.  It also creates some other problems when you have a custom filter function, as described here:

http://www.telerik.com/account/support-tickets/view-ticket.aspx?threadid=781390

I recognize that you would not want to change the default behavior since it would be a breaking change, but could you add a flag to toggle this behavior off.  You could add a property called "DefaultTextToValue" which is set to True by default, and if you set to false, the display would remain blank until the text value was set by the databound event.

Right now other JS UI libraries allow the autocomplete dropdownlist to dynamically size based on the returned content. KendoUI sets the width to the width of the input box. I understand this looks nice but doesn't work for all business aspects. An example is my company needs to enter search criteria but the return results is the code and description. Since this can get longer than the input box the text is wrapped. This confuses users as they don't know where one item starts or ends. We use to modify the source files to fix this but the Q2 release changed a few things and stopped us from doing this.

Adjust KendoDropDownList so that when the mouse scroll wheel does reach the end of the list the focus does not jump out of the control and scroll the form.

Add a way to check if the current AutoComplete value would be in the suggestions. Since the widget already searched for the value to see if it is in suggestions I would prefer to be able to check the result of that search. Something like calling kendoAutoComplete.search() but not have it affect the UI - just tell me if it was found or not. Is that possible?

I want to be able to alter the UI if the user has entered a value that is not detected in the suggestions to let them know it is not a valid value, and it seems silly to have to manually see if the value is in the datasource (and handle the filter variants 'startsWith' and 'contains') when that is already being done by the widget. So, I'm just looking to detect whether the search done by the widget found the value in suggestions or not.