Program to Inventory software on Clients

Looking for good software that would allow an administrator to inventory installed software on client and server machines. Was given a job to find out how many copies of popular software packages are installed, and what the those packages are. It was easy to keep track when there were only 10 pc and 2 servers, but now we have grown to 50 pcs and 12 servers. The job is now getting out of control.
I am aware of Microsoft’s SMS, but thought that package to be too large and expensive for a small buisness to use.
Any help would be appreciated.

Thanks,
jwatson@psi-sc.com