I use
http://www.statcounter.com/ I like it because it is free; and it is not just a counter but it tracks all my statistics; like how/where people found me, how often people visit, and for how long. It also tracks IP addresses and search engine key words... lots of cool stuff!
It also tells me not just how many hits I get; that's really a page-load statistic... so for example if you have a tracker and it says you have 1000 hits in one day; chances are that is really just 300-500 individual people... and they loaded the page more than once; like when they leave to visit a link on your page and then return back. It also will tell me who is a returning or regular visitor; and it makes pretty charts and graphs for you! SO it's very accurate.
I also like that you can make it invisable. I'm not really a fan of visable counters...