<p>I asked <a href="https://stackoverflow.com/questions/168661/javascript-table-manipulation">this question</a> a while back and basically the project almost consists of reproducing excel in the browser.  We want people to input data in an excel-like way.  The question i have is, what is the best control to use?  Should i use a regular table, and then append columns to it, or should i use a datagrid and flip it XtoY?  What approach would you take?</p>

<p>Thanks for any help.</p>

Option 1: Check out the Silverlight option to develop your application. And it had a good Excel like DataGrid which is rendered at the Browser lever and you can have async  calls to server at any point of time you want to persit a change.
Option 2: There are many
datagrids
available in WPF and you can get a high performance application using .NET3.5, and it is possible to host this as XBAP application.
Option 3: Typical ASP.NET with AJAX enabled Datagrid