Our sysadmin has tried AssetMetrix, and apparently it gives a lot of false positives -- things like Windows Media Player that you generally don't need to care about.
I'm tempted to write some sort of simple software asset database, that lets you record info on the licenses you have. The next step would be to have a little tool that you can run on all your computers (as a scheduled task, perhaps) and find out what they're running. This would be helpful to let you know whether your software licenses match what you're using, so you can avoid having to suddenly buy lots of licenses when some supplier or other decides to audit you.
Does something like this already exist? If not, would you buy it?