Google Spreadsheets 5

Wow, Google Spreadsheets (technically Google Docs & Spreadsheets) is impressive.  It's like a lightweight, web based MS Excel.  It doesn't have a lot of the more sophisticated functionality that Excel has, but it has all the basics like sorting, formatting, graphs, worksheets, etc.  

More importantly, it has sharing, so you can have multiple people working off the same doc, available at a single URL.  It's pretty powerful for group profects.