EditGrid
Editgrid is a free web-based online spreadsheet which allows you to create and share spreadsheets documents. you can collaborate with your team, publish your spreadsheets and even power them with external data.
http://www.editgrid.com/
Gnumeric
Gnumeric
http://www.gnumeric.org/
Google Spreadsheets
Google Spreadsheets
http://spreadsheets.google.com/
KSpread
K desktop environment homepage, kde.org
http://www.koffice.org/kspread/