Google Analytics or Woopra if you want too have more fun and want to see your visitors visit your site LIVE.
I use www.histats.com and it's free and I am very pleased with it. Another program that's just awsome, but costs $35.00 a month is www.Whoson.com It's more then just a stat retriever. Check it out.
Use Google analytics if you want to have in depth knowledge about the traffic of your website/blog. Its free of cost but really worthy to have a look.
Google Analytics is the best and free. You may also try statcounter. Statcounter is pretty fast in gathering statistics. The stats update in 1-2 minutes after visit.