There are too many methods to make an auto complete text box in asp.net
You can use JQuery (Use jquery for Auto Complete), Ajax Auto complete extender and so on. If you will search on internet you will find so many examples which are using JQuery or Ajax Extender to show auto complete on websites.
I had searched on many sites I had tried so many examples to populate auto complete list but, unfortunately, I am not able to find an efficient auto complete example.
Finally after searching for many hours I had decided to write my own code.
My example is using an asp.net C# to show auto complete. Here, code goes
Run and try typing some numbers or text. You will find an auto complete list on page