If there is another thread for this, I wasn't able to find it.
If you haven't seen it yet, you should check out Google Docs. Google has set up an Office Suite and made it available online, for free. I used it to create a spreadsheet to calculate how much money we spend on gas per year.
Nesman's Gas Prices Computed by Mileage
You can choose to share your documents with specific people, or publish it and make it available to everyone. You can create spreadsheets, documents, and presentations (read: Excel, Word, Powerpoint). These documents are connected to your Gmail account and accessible anywhere without having to install any software; let alone making sure to have the same version of the software.
I found the spreadsheet program easy to work with, and I'm not a big Excel user. (This may have been to my advantage)
