StumbleUpon, every blogger loves this one! Its a great source of traffic for every blogger, big and small. The best part of StumbleUpon is that it gives you free traffic and is not really into the crowd mentality like Digg or the other media sites. Though hard to monetize, it builds a brand by putting it in front of a million people. Thats very important if you are looking forward to become a problogger or a popular one. Here is a screenshot of my traffic: