PHPExcel provides classes which allow you to create Excel 2007 files in PHP. This requires PHP 5.2 and php_zip extension enabled.

Some of the features this class set provides:

• Setting spreadsheet meta data (author, title, description, …)
• Multiple worksheets
• Fonts and font styles,
• Cell borders
• Fills
• Gradients
• Adding images to your spreadsheet

A code sample showing the usage is available at:
http://www.codeplex.com/PHPExcel/Wiki/View.aspx?title=Examples

Link to Project page: CodePlex - PHPExcel