Open Educational Resources

The CC LibGuide has additional options for places to find CC licensed works.

Pros: One of the largest OER repositories, covers multiple disciplines, allows for sorting by education level, reuse options, and by standard.
Cons: Rating system is a bit unclear.

Pros: High quality textbooks for introductory level college courses.
Cons: Little content for upper level courses. Not much coverage in the humanities.

Pros: Large collection of textbooks with published peer reviews by professors, does include some upper level/graduate textbooks, easy to use interface.
Cons: As the name suggests, the content is limited to textbooks.

Pros: There are lots of filtering and limiting options when searching, wide range of disciplines represented, wide variety of material types.
Cons: Search interface is a bit clunky.

Pros: Searches content from over 60 different sources, you can sort by license type and type of resource.
Cons: Can't sort by education level.

Pros: Simultaneously searches multiple repositories, could give you good ideas of other repositories to look in.
Cons: Search interface is difficult to use, search results sometimes take you to the main page of different repository and then you have to redo your search, not easy to determine licenses for items.