This is the next level of the plain old link exchange. The basic principal is same - you advertise my blog, I advertise yours - but the way of implementing this is interesting. You pay for this advertising with Entrecard Credits, that you earn for free by networking (a.k.a. visiting blogs and dropping your card for other bloggers).

The Hidden Network is an ad network concentrating on jobs classifieds. It’s not your typical ad network or a job board. Jobs you post on Hidden Network appear as ads within a network of some of the most influential Web publications read by talented programmers. You can call it kind of Monster fused with Google AdWowrds.

AdGridwork is a free contextual and text links advertising network. It is link exchange reborn in Web 2.0 style! If you have a site or a blog and can’t afford to advertise on Google AdWords, Yahoo Overture or MSN AdCenter, then this is an option for you. You display ads for others and others will display ads for you.