Specifically, I"m looking at parked domains - either buying or creating and I need to know how much "passive" traffic these names are getting... also - are there any other worthwhile sites out there besides Sedo for buying quality parked domains?
Alexa can give you a fairly good "ballpark" idea. Compare the Alexa rank to that of a site that you know the traffic totals and work it out. This is not a perfect system, but it will give you a rough idea.
for free programs google analytics is the bomb. but if you're hosting it yourself you should have a webananalyzer. that is more useful for checking robots and crawlers.
Google Analytics is good, and free. If you host with a good host, they usually have AwStats and Webalizer included in the hosting package, and you don't have to install anything. Check out your CPanel.