There are many different online office programs but almost none of them are integrated in a suite. Google finally released the first progam in their office set: Google Spreadsheets. Word competitor is going to launch pretty soon too (Google Writely).
The spreadsheets are very fast and allow you to do pretty much everything you could do in your favorite Excel (axcept for Graphs but it's coming too). But lets put that aside. The most important and exiting thing about this new product is that it allows the user to share his/her spreadsheets with others (allow to edit or just view). Me and bla played around with that feature and it's amazing (you even have a little chat window where you can discuss what you're doing).
I personally really like the idea of Web 2.0 Office (I know I just said The Curse Word) and if some of you are the same as me you will really like it as well.
And to sum that up... IT'S FREE !!! :) (No need to pay for MS Office anymore [like anybody did anyway])
P.S. If anybody need to try it out then just tell me and I'll invite (they are in limited beta and general invitations might be out by now).