Wikipedia Articles Sure, they don't pass over Pagerank or SEO value, but you can't beat the "targeted" traffic
unpaid one way links have worked best for me so far. with some paid links, i just wasted money. some worked great but if you pay for links, you have to keep paying to get the benefit
Correct, very few people can get the ROI they need to make paid links viable. Usually sites selling products that have a high ROI can get away with this. Informational sites will usually always spend more than they get back. This of course takes in not only the costs of paid link, but the taxes you pay on your revenue at the end of the year, plus hosting and domain fees and any other forms of advertising you might use that require monitary backing.