Other
Western Grammar: Prepositions
This resource offers a brief definition and examples for the use of prepositions. Hyperlinks to other parts of speech.
Online Writing Lab at Purdue University
Purdue University Owl: Prepositions of Direction: To, On(to), In(to)
Maintained by the Purdue University Writing Lab, this tutorial focuses specifically on the three prepositions mentioned in the title. After a general introduction, the site specifically discusses each preposition and presents examples.