This is really a critical error. You MUST know where ALL your visitors are coming from to be successful in IM. I have thrown up a blog or two in the past targeting certain keywords, only to find that folks were arriving on my blog from totally different keywords, AND converting WELL! Needless to say, I worked on optomizing the site for those keywords and exponentially increased my sales and profit!
The free tool I use is Site Meter - Counter and Statistics Tracker (Not an AFF Link!) This site provides virtually EVERYTHING the beginner or even the more advanced marketer could need. It tracks hits, referring pages, outclicks, entry pages, countries, and so many more stats. And that is ALL in the free version.
You can setup unlimited counters for each of your sites. Check it out - I highly recommend it!