There is a free book on assembly language by Dr. Paul Carter. It's based on NASM.
http://www.drpaulcarter.com/pcasm/
There are some interesting collections of sample programs at
- http://cs.lmu.edu/~ray/notes/nasmexamples/
- http://www.csee.umbc.edu/portal/help/nasm/sample.shtml
- http://forum.nasm.us/index.php?board=3.0
- http://www.fifi.org/doc/nasm/examples/
