I've been working with Microsoft Office SharePoint Server 2007 for a while now (participating in the beta tests and helping customers deploy the RTM version). The previous version, 2003, came in only one flavor. The 2007 version comes in several editions, and some of my customers were confused as to what features came with which editions. I found that I did not have a good handle myself, so I did a little research to find out.

I found a very good resource here:
http://office.microsoft.com/en-us/sharepointserver/HA101978031033.aspx

This site contains an Excel spreadsheet with a fairly detailed list of MOSS and WSS 3.0 features broken out by feature type, Management, Business Intelligence, Search, etc.... This is a direct link to the spreadsheet:
http://office.microsoft.com/search/redir.aspx?AssetID=XT102011901033&CTT=5&Origin=HA101978031033

Update
I also found a web-based version of the same information here:
http://office.microsoft.com/en-us/sharepointtechnology/FX101758691033.aspx