Here are some links my flight instructor has sent me over time to study from:
All 200 questions (50 of which will be on the test) from TC
Robyn's Flying Start - AWESOME study guide w/ reference links
Pilot Sense - you have to create an account, but this is a GREAT practise test, and keeps track of your responses, with links to relevant sections for futher study.
OFF Training - this links to the PSTAR exam section of their site.
Principal Air - The questions in each section of the PSTAR are shown individually, with links to the correct answer and also relevant references.