Microsoft Reader 2.1.1

System requirements
Processor Pentium 75 or higher microprocessor
Memory 16 MB RAM
Hard disk Approximately 19 MB free hard drive space (Microsoft Reader is 3.6 MB, but additional hard disk space is required for installation)
Operating system Operating System-Microsoft Windows® 98 platforms, Microsoft Windows NT4 SP6, Microsoft Windows 2000 platforms, Microsoft Windows XP, and Microsoft Windows Me.
Display VGA or higher resolution monitor and video card capable of displaying 16 bit color
# Other devices Microsoft mouse or compatible pointing device
# Microsoft Internet Explorer 4.0 with Service Pack 1 or higher

http://www.microsoft.com/reader/downloads/pc.asp

One of the best out there in my opinion. The encarta pocket dictionary is an amazing addition, along with the ability to for it to read the text to you.
:D

The only thing strange is the format (.LIT)... but once you get used to it, Microsoft reader rocks.