I would like to add a couple things not mentioned. While there isn't the equivalent of man -t <topic> for info pages you can enter "info:<topic>" in the konqueror web browser. These pages were produced by your distro ahead of time. Also there is a local server called "info2html" that can be used to translate the info pages to html for live browsing. This is how the info:<topic> pages were produced.
I will often install the source (either .tar.gz or .src.rpm) files and produce manuals from the source. I did this for the "Bash Reference Manual", "The Gawk Manual", and "GAWK: Effective AWK Programming". If you are new to GNU/Linux, printing out the Coreutils Manual is a must.
Also, take a look in what is available in the /usr/share/doc directory tree.
find ./ -iname "*.dvi" -o -iname "*.htm" \
-o -iname "index.html" -o -iname "*.ps" \
-o -iname "*.pdf" | less
I bet you would be surprised how much documentation is there.