Because OpenOffice.org is such an obvious and excellent replacement for Microsoft Office (including Word, Excel, and PowerPoint), it's easy to forget that there are other alternatives. One of the great things I keep coming back to when I talk and write about Linux is that we do have alternatives, some costing no more than the time it takes to download and install them.
When it comes to spreadsheet programs, your Linux distribution CDs likely came with a few spreadsheet programs. The primary candidates are Gnumeric, KSpread, and the program we just looked at, OpenOffice.org's Calc.
Both Gnumeric and KSpread are certainly worth a look, but I've found Gnumeric to be particularly good when it comes to working with Excel spreadsheets.