One of the sites you often see mentioned in the Microsoft Port 25 blog is CodePlex where Microsoft technology related Open Source projects are found. I pop over there from time to time to see if there are any interesting projects that might be useful in my own work. I found PHPExcel 1.6.0 on my most recent visit. It was last updated on Feb. 13 and provides PHP classes to read and write Excel 2007 spreadsheet files.
The examples section provides simple to read and understand PHP code to get a handle on how to use the classes as well as 16 sample XLSX sample spreadsheet files to test interpreting spreadsheet features such as formulas, conditional formatting, and page breaks.