CheckBox 
TextBox 

Adding a "select" when user choose one of the hint in AutoComplete to help field-linking.  More detail and implementation about the idea in here: http://www.kendoui.com/forums/ui/autocomplete/suggestion-about-select-event.aspx

I really like what you've done so far and I think you're very close to the top if not already there in terms of being an HTML5 UI leader. The one thing your data visualization set is missing is a map. A simple map to show chloropleth data, basic paths etc is well within your reach and would round out your DataViz offering.

Please ensure when altering the treeview (adding checkable items) that it supports multi level and tri state parent nodes (shows as partially selected when not all child nodes are selected)

Similar to jquery mobile, it would be useful to handle below events
- touch (with fingers, directions)
- tap
- tap hold
- swipe (left / right)

Currently a datasource model field can have a "validation" definition, where each is treated as a validation rule. This allows for a custom rule to be added (e.g., a function to check the field value is not a duplicate), but there is no way to define the associated custom message - it would be nice if we could define "messages" to go with the rules (or maybe specify a validation object?).

It would be nice if the grid pager checked to see if a new row has been added, before allowing the page to be changed. This results in a blank row in the grid, even if the row contains a required field. Maybe ask confirmation from the user about navigating away and remove the row. 

Is Kendo ui support Barchart and Line chart in Tablet Pc? In IE 9 and chorme kendo ui Charts are working properly.but in Tablet Pc its not working.can i reply soon?

I need to know this if I m using Kendo UI, is there any possibility so that i can use all Grid API's on same HTML page ?

Add optional scrolling to Chart like Telerik RadChart Scrolling:
http://www.telerik.com/help/silverlight/radchart-features-zooming-and-scrolling.html

And/Or add a paging feature to the Line Chart that allows the user to page from right to left through data. Use the paging feature of the datasource to allow huge datasets to be viewed in increments (querying pages of data for the chart as the user pages from right to left) for performance.  For example, if a years worth of hourly data is requested, page by month through the chart and query the data from the datasource one month at a time.  This could work nicely with a grid configured for paging using the same datasource to display the data and chart in sync on the page.

Add TickDistance, AutoRange and Step to the line Chart like the Telerik RadChart.  When querying a web service and charting a dynamic/variable number of values, the current chart results in grid lines too close together and overlapping x-axis values.  This would space the grid lines and labels based on the number of values and available space.  This is from the RadChart documentation:

The TickDistance has to be used together with AutoRange. When AutoRange is set to True, the axis Step value is calculated depending on the data range, the available space and the TicksDistance value. Since TickDistance defines the minimal distance between two ticks, increasing its value will cause the Step value to be increased too.

Provide a bundle for TextMate that includes snippets and code coloring.

Do we have ReloadOnshow="True" property for Kendo UI Window too.......

query string issue with Kendo ui window(Every time we open a kendo window the Query string should get Updated Instead it not happening)

We have been migrating from using the RadControls for ASP.NET Ajax to the Kendo UI suite, and have found the controls very useful.
However there appears to be a slight discrepancy between the parsing capabilities of the two libraries.

eg.
http://demos.kendoui.com/web/datepicker/index.html
http://demos.telerik.com/aspnet-ajax/calendar/examples/datepicker/custompopup/defaultcs.aspx

If you type 1-1 in the RadControl demo, this is correctly parsed as 1-Jan-2012
If you type this in the KendoUI demo, this is not parsed correctly

It would be great to have the same flexibility of parsing of the dates as per the RadControls?

See http://www.componentone.com/SuperProducts/PickerViewiPhone/

Most web application today must run in different environment, people from disable to different language I would like to suggest that including the right to left and ARIA.

Please consider implementing a Multiselect control similar to how this jQuery plugin, Chosen, works. Look at their Multiple select and Multiple select with <optgroup> examples:

http://harvesthq.github.com/chosen/

For an example, check the Yahoo weather app on iOS. Click (i) to add/remove/reorder locations.

For another example, check the Yahoo stocks app on iOS. Click (i) to add/remove/reorder stocks