We're using Sysaid from Ilient at the moment (http://www.ilient.com). It does inventory management, work/maintenance tracking and web-based fault reporting as well. I've been using it for about 9 months now and haven't had any problems (apart from persuading staff to use the fault reporting rather than leaving illegible post-its all over my desk )
You have to deploy a small client app to each PC, but it comes with a program to push this out over the network, so no legwork involved. It records serial nos, installed software, OS etc and will do exports to CSV files.
It's free to use for up to 100 machines and 2 admin accounts, which is fine for us but I guess won't suit everyone. It can run on its own internal database, which suited me as I haven't got an SQL server running at the moment.
