I just want to throw out there to give some thought whether you have anything you can 'sell' in exchange for a link.
I just got contacted by a private school wanting to buy a 4 letter domain I own that I've been too lazy to do anything with.
After I got over the dollar signs, I've offered them the domain for free - as long as they give me a link for min. three years. They even have a page that's reasonably appropriate.
I backed the email up with some proof that my site is legit (pointed out some media mentions) so that a school could reasonably link to me.
I haven't heard back yet, but I expect they'll bite.
I've actually got a dozen or two 4 letter ccTLD domains that I'm not using. Perhaps I'll go googling see if I can find some decent sites that might be interested in a swap. (and perhaps you can use a similiar technique if you've got domains you're not using).