The counters are usually Java applets, and for those of you that don't regularly follow tech news, Java has been under attack recently. There are a lot of security holes that have yet to be fixed. Not sure where this will lead, but using Java applets is a security challenge for any site nowadays. Maybe HTML5 holds some promise to create this functionality without the need for plugins??
For smartphone use, I found a nifty little widget called "Days Left" that you can add to your home screen. Customizable in size, color and displayed text. Caveat - I found this in the Android Play store, so not sure how you iPhone users handle widgets...