Microsoft offers several free VBA references.  Each is available for download as a .chm (Help) file and as an online references.  These references contain conceptual overviews, programming tasks, samples, and references to help you  write VBA for Microsoft Office applications:

Available are:

• VBA Language Reference for the Office Object Model
• Excel VBA Language Reference
• Word VBA Language Reference
• Access VBA Language Reference
• PowerPoint VBA Language Reference
• Outlook VBA Language Reference
• Publisher VBA Language Reference
• FrontPage VBA Language Reference