As an example I have started a Plug Board myself: Add Your Ad For Free where you can enter a free advert and this will go live straight away.
Now I can't tell you if these Plug Boards will bring you much in the way of referrals but I'm testing them out and have been leaving my ads all over the place.
I didn't, back then, realise that links were also useful for things like PageRank but remarkably Mikes Money Making Mission soon got a PageRank5 because of me doing this. My PR has been thumped since them because Google doesn't like the selling of links which I was once, innocently, doing. But that's a whole different story.
I'm sure that big established bloggers will sneer at the thought of Plug Boards. They will talk of writing articles and other ways to get traffic and links.
I'm sure these 'other ways' are probably more effective but a link in is a link in.
I'm away now for about five or six days on business so, until then, happy plugging!
Good luck,
Mike.