Rice Connections: Book with great resources - also great source for questions.
http://cnx.org/content/col10522/latest/
Introduction to Statistics Textbook
http://onlinestatbook.com/
CK12.org Flexbook
http://www.ck12.org/flexr/flexbook/904
CMU Stats:
https://oli.web.cmu.edu/openlearning/forstudents/freecourses/statistics
UCLA Statistics E-Book - Great Site with Questions too :)
http://wiki.stat.ucla.edu/socr/index.php/EBook#Learning_and_Instructional_Usage
Understanding Statistics - Great site with Questions too :)
http://www.abs.gov.au/websitedbs/a3121120.nsf/4a256353001af3ed4b2562bb00121564/848febd925a6b134ca2575dd0003a5f2!OpenDocument
WikiStatistics book
http://en.wikibooks.org/wiki/Statistics
CC Statistical Questions:
http://www2.gsu.edu/~dscbms/ibs/qcontent.html
List of CC Statistics Books
http://collegeopentextbooks.org/open-textbook-content-/open-textbooks-by-subject/statistics-a-probability.html
----------------------- The following are open source but the content is not as good as the above sites
Open Learning University - UK
http://www.open.ac.uk/openlearn/science-maths-technology/mathematics-and-statistics/statistics
Virtual Laboratories in Probability & Statistics
http://www.math.uah.edu/stat/
MIT Open Course in Applied Statistics
http://ocw.mit.edu/courses/sloan-school-of-management/15-075-applied-statistics-spring-2003/
R Programming WikiBook
http://en.wikibooks.org/wiki/R_Programming
R Tuturial
http://www.cyclismo.org/tutorial/R/index.html
Other Links - Be wary of copying and using material IN assisments due to copyright issues (see links below) - however, you can link to these sights
CAST - England Interactive Resources - Amazing Resource - However, you can only link to the pages/applets. You cannot pull or copy content and use it in the assistments.
http://cast.massey.ac.nz/collection_public.html
Causeweb.org - Good general site that catalogs a variety of statistical learning materials.
http://www.causeweb.org/resources/
RIce Virtual Lab in Statistics - Good general resource for learning materials
http://onlinestatbook.com/rvls.html
StatTrek
http://stattrek.com/
Seeing Statistics
http://www.seeingstatistics.com/
Data Sets - great to use with R & Rweb.
Pre-Installed R data sets - list of available R data sets
OzDASL - Australian Data Sets
QELP - Environmental Data Sets
UMass Data Sets
AP Exam Material
Breakdown of Free Response Questions - PDF Format
Link to Breakdown of past AP Exam Free-Response Questions by Topic
Link to past AP Exam Free-Response Questions
Link To Released 1997 AP Exam - Useful for Multiple Choice Questions
AP Course Description - Has 18 example multiple choice questions
AP Review Exam Tips - This page has tips for different topics - find your topic and keep the tips in mind as you create your assistments