Selling links is a great way to make a little profit on the side but requires you site to have a lot of traffic and pr. Many sites have a sitewide link area to add them in. It's really your choice. You can either sell links or do link exchanges for more traffic.

Here are the prices that you could sell links based on PR. There is room to sell them more if you can prove that you have great traffic at the site. Not only that but also if there is a high demand for people buying link for the type of site you have then you can boost the price. It doesn't seem that you make money but you have to understand that you can usually have 10 to 20 of them each month.

Pr 0 = cannot sell

Pr 1 = $1 per month

Pr 2 = $2 per month

Pr 3 = $2.50 to $3 per month

Pr 4 = $ 4 to $6 per month

Pr 5 = $9 to $15 per month

Pr 6 = $15 to $20 per month

Pr 7 = $50 to $200 per month

Pr 8 = $100 to $1000 per month

Pr 9 = $1000 to $5000 per month

Pr 10 = $5000 to $20,000 per month

The best and easiest place to do this is at http://forums.digitalpoint.com/ . There is a high traffic area to sell links in that forum.