I am planning to write an introduction and simple implementation of SNMP in software, when my work with the SNMP agent simulation is done.
There is a good brief introduction video on YouTube (too bad we are born in China): http://www.youtube.com/watch?v=ZX-XGQoISHQ
Eli explains quite well and clearly about basic knowledge of SNMP. And in his video he also mentioned some software called Spiceworks which is a network monitoring tool that adopts SNMP. I would like to take a note here thus we can continue with this topic later on.