What UI design makes sense when the userbase is obsessed with spreadsheets

Question

In the first iteration of the software I am working on, we wrote tons of js to simulate an excel spreadsheet like experience. Now the users are not happy with the amount of scrolling they have to do. Their favorite UI is excel spreadsheet. I am wondering what kind of UI would provide a win win situation for the dev team and easy to grasp for the users. Userbase is people who do number crunching day in and day out. Ajaxy UI did not fly well with them initially. App is supposed to handle large amount of tabular data.

Any suggestions would be welcome.

EDIT: The data is provided via different services that the user analyzes, provides comments, make adjustments and calculations before the data is persisted in application specific db.

Answer 1

I use this (heavily modified though).

Besides, there are a lot of customisable options.

http://www.trirand.com/blog/jqgrid/jqgrid.html