The HeadCounters WordPress plugin adds a widget that displays how many visitors are on your site at that moment. Now Configurable!
Wondering how many people are on your page? You can finally know! No longer will you be kept up all hours of the night, wondering... wondering... wondering... how many people are on my website? HeadCounters answers the eternal questions of (internet) life: Does my site have any visitors? How many people are here right now? Am I all alone? With HeadCounters, now you'll know!