I've found for us on Wikipedia is to find topics in your niche that have a list reference ideally that has images next to it. IF you can provide an image, its an image link which we have found helps with google image ranking but also you get a text link in the External Link section and normally we link that as the keyword (works well for products if you're in e-commerce)
So example if I was selling red matt paint if there was a paint list and a picture of red paint was missing. Id submits a link to my paint and then in the external link reference id cite my url with a link on the product i.e red matt paint.
I've found this has worked well for us as we obtain two links on one page, it adds to the resource and 9/10 is hardly moderated!
If you are in a super focused niche (like we are) you may have to be creative and expand your search. So if I was only selling wooden spoons, if my spoon was made of oak, id try and find a reference list to oak or wood and include a sample picture of our product. It's hard as you may have to go 1 or 2 layers outside your product these sort of links I find do get a bit of moderation.
