I was talking to a customer today.  Whereas some of their business uses BMC ADDM to do a discovery of compute resources, another one of their locations uses a free open source tool that is custom tailored to querying ESX V center.  IT is called RV Tools available here:

RVTools - Home

This is a simple .NET 2.0 Application that can connect to a variety of ESX versions and pull out data about these servers.  The data they shared was quite detailed, including information about the storage volumes linked to each VM.

I had a customer who used RV Tools to populate their CMDB but I thought it was an ESX component and didn't realize it was an open source tool, thanks for the link.

I looked into the documentation of this tool, and it can be run to dump data to a csv or xls using a command line interface in unix, and unsurprisingly, can also have multiple exports automated with a batch file.

Take a look at page 80 through 84 of the documentation here for some examples:

http://robware.net/download/RVTools.pdf

I use RVTools to extract the VM data from two data center sources and then combine the extracts using Excel and Power Pivot.