I came across Calibre recently and it's a very good program for reading eBooks on your PC or Laptop. It can be used with many different formats (non-DRM*) and there are many sites that now offer free eBooks that are out of copy-write. It even converts from one format to another. Or as they describe it:

calibre is a free and open source e-book library management application developed by users of e-books for users of e-books. It has a cornucopia of features divided into the following main categories:
  • Library Management
  • E-book conversion
  • Syncing to e-book reader devices
  • Downloading news from the web and converting it into e-book form
  • Comprehensive e-book viewer
  • Content server for online access to your book collection
Available here.

*DRM = Digital Rights Management