Perform daily/weekly tasks to earn points towards your next level. Each level unlocks gear and equipment for your avatar as well as a new title. Don't be your "Average Joe" when you can be a "Global Super Hero" and make a difference.
Dribbble - Progress Bar for game by Max Litvin
Loading Bar by Wasim Shahzad
Another UI consideration. CSS has made quite the progress, hasn't it? --> demo here