Updated: as of July 2, 2011, here’s how paid advertising appears on LessonIndex.com:

Among product links, products which are offered for sale by advertisers appear first within each section, and advertisers’ links appear first under each unique product (before unpaid links to other retailers). Advertisers’ links appear “slightly larger” within the directory itself (depending on your browser settings, these links might also appear to be in bold).

These advertisers’ links are “affiliate program links” — if someone clicks on one of these links and then buys something from the merchant, I am paid an advertising fee (some technical details are discussed in the Privacy Policy).

Publishers and retailers do not need to pay for their products to be included in the LessonIndex.com directory; an advertising arrangement affects only the position of a specific link. Listings for free products are included for free, and should be clearly marked with a green text tag: (Free)

The paid advertisers whose links appear most frequently are: eNotes, CurrClick, TeachersPayTeachers (TPT), Teacher Created Resources, and ChristianBook.  In general, products sold by these merchants are clustered near the top of each section.

Links to other merchants are shown for free; these include links to Amazon, Prestwick House (PH), Teacher’s Pet (TP), DedicatedTeacher.com, GoTeachIt, BMI, ChildGraphics, Shmoop, Center for Learning (CFL), ECS Learning, Applied Practice (AP), Walch, TakingGrades, and many others.

I include many more unpaid links (than paid links) because my primary goal here is to provide a “relevant and useful” directory for teachers, and an incomplete directory usually isn’t very useful.