I am using Notepad+ from past couple of years, it is the best lightweighted text viewer I have used so far.
PROS:
Free and opensource
Plugins right into application like text compare, guid generator, hash generator
Supports formating and color highlighting for wide range of programming languages, identifies programming language by file extension.
Hexadecimal and unicode support
Lightweighted
Regular updates
Files persists in cache even those files are not saved , good if you accidently close application
Feature to set your favourite directory for frequent folder location.
CONS:
Can’t think of any.