What is a good cost effective IT asset management solution?

Solution 1:

http://www.ocsinventory-ng.org/

Automated with agents to monitor computers (hardware and installed software). Agents available for Win/Mac/Linux.

I've used this solution myself, and I'm very happy with it.

Solution 2:

I have had a lot of success with GLPI. It's a nice looking, easy to use web-based asset management system.