Looking for something that looks nice, is flexible with reporting, and can track everything you would expect with good IT asset management.
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.
I have had a lot of success with GLPI. It's a nice looking, easy to use web-based asset management system.
You could try NetSupport DNA
Tracks all hardware and software, and will notify you of changes. It also includes an application stopper and internet filtering.
I have been using Spiceworks for a few years now and I absolutely love it. Doesn't require an agent, as it uses WMI, so only a firewall rule and Admin privileges on the box.
I've been testing lansweeper at my work and we're extremely happy with the product. Some of the nicest features: free version, custom reports, custom fields to track assets or other important info, easy to install. Currently our test is up to 300 computers and servers. It's working great. Highly recommend it to others.