There is e.g. Writing A Useful Program With NASM and of course the obvious http://www.nasm.us/doc/nasmdoc3.html.
There are a couple of sample programs at http://www.csee.umbc.edu/help/nasm/sample.shtml
If you are looking for a more general introduction to assembly programming there is The Art of Assembly Programming and the wikipedia page on NASM references Assembly Language Step by Step by Jeff Duntemann.