I sell calculator type website plugins to vendors in my niche (including my competitors). The service is about $200 a year. There's been large pressure in that industry recently - that end of my business is floating to a great extent due to my existing relations with my clients. But that won't last forever. So I'm dropping my price to $50 - if they give me a link to my main money site from their site. These people are all direct competitors to me.
Secondly (again, I already detailed this) I recently found an academic that wanted a custom calculator created. They wanted it released as an informational type of service. I partnered with them, they gave me the calcs, I created the software. I'm going to release it via GPL. Then the academic is going to do link dev for me. Not deliberately - they just want to promote this information calculator that's their baby.
Another example of content I'm using to gather academic links is some research data I came across. I've purchased the rights to it (this type of stuff is normally proprietary) and am publishing it on my site. Then I light up the emails with 'visitors to your .edu site who are doing research may find this information of use in their research.'. A few bite.
None of these are new ideas, they've been around for years. But no reason why they won't still work.
Now I'm thinking I should consider if there's any type of calculator that would be of interest to academics in my field. Nothing comes to mind immediately, but it's something I'll keep in the back of my mind.