5 Answers, 1 is accepted
Our textbox control does not support auto-complete out of the box. You should use RadDropDownList in case that you want to this feature. The RadDropDownList supports two modes of auto-complete AutoCompleteSuggest and AutoCompleteAppend. I suppose that in your case you should use the AutoCompleteAppend mode.
Hope this helps.
Peter
the Telerik team

2016 Update for those who may find this while searching for a way to continuously update a append/suggest list from a large database. Or, "How to dynamically fetch data from the database while typing?"
Server side auto complete for RadDropDownList
http://www.telerik.com/support/kb/winforms/details/server-side-auto-complete-for-raddr
By Georgi Georgiev
the example uses the Entity relationships classes for the database access. It's a pretty nice piece of code. :D
Thank you for writing in the thread.
Indeed, the approach suggested by my colleague resolves a scenario for dynamically fetching data as you type. In fact, as stated in the article the solution should work with any IEnumerable collection.
The link you posted appears to be incomplete, here is the correct one: http://www.telerik.com/support/kb/winforms/dropdown-checkeddropdown-and-list/details/server-side-auto-complete-for-raddropdownlist.
I hope this helps.
Regards,
Hristo Merdjanov
Telerik

Thanks for providing a corrected link.
That article resolved something I had wanted to do for quite some time. Users are beginning to expect that Google-like response to list searches. Pulling all items from a million+ record table to populate a search list isn't really practical.
The link I had posted was slightly different than the one you provided. Same article though.
http://www.telerik.com/support/kb/winforms/details/server-side-auto-complete-for-raddropdownlist
Thank you for writing back.
I am glad that the suggested approach in the KB resource fits your scenario. Regarding the links, indeed, they point to the same article.
Should you have further questions please do not hesitate to write back.
Regards,
Hristo Merdjanov
Telerik