Free Advertising Network
It's a free blogging network that helps you build traffic, get more readers, and network with other bloggers. You put a 125×125 widget on your blog and you can earn “EC credits” when members visit your blog. You can use the “credits” to purchase advertising on other blogs in their network.

Benefits of dropping cards
  1. Dropping a card earns you 1 Entrecard Credit each time you drop.
  2. Dropping a card for someone increases the chances that they will visit your blog.
  3. It is a great way to see what other bloggers in your niche are talking about.
  4. It is a great way to discover new blogs!

If you already in entrecard network then to advertise in other sites you need credits,now entrecard giving away 5000 credits($15 value) free if you write a review about entrecard on your blog.To know more about this contest click here