WinAudit is a freely available app from those nice folks at Parmavex Services across the Pond in Great Britain. This nifty lil' tool will snap on a rubber glove and give your PC a very thorough examination - telling you more than you ever wanted to know about your PC. I tend to pare down the options to installed hardware, software, and sytem uptime.
Netzup is a frightfully clever app that works remotely, exploiting null connections, IPC$ shares, and the like. It can silently install applications and execute programs. Also, can also enumerate the remote PC's registries and gather a list of installed software for auditing purposes.