It is probably worth investing in two different college handbooks, one general and one interpretive. The general handbooks are not particularly interesting to read, but provide lots of useful facts and figures on nearly every college and university in America. Virtually all of these books are of high quality. The College Board, Princeton Review, Barrons, and Peterson's all publish books that can be purchased from their respective web sites. The interpretive guides are more chatty of tone, giving you a sense of how a school feels. They are much more fun to read, and are worth having for that reason alone. When you are trying to find the right match, an interpretive guide is a very good place to go. The Fiske Guide to Colleges by Edward Fiske is our favorite, but the Princeton Review's The Best 351 Colleges is solid, too.
Unless you are a naturally gifted tester, you will need to prepare yourself for the SAT Reasoning Exam and the SAT Subject Exams. Since you are coming from an American school system, virtually all universities will require those of you, including the US, UK, and Canada. The Student Services Office keeps some of these books for your reference, but it is well worth buying your own. The ASL bookstore stocks many of them, and others can be purchased online through Amazon, The College Board, Princeton Review, and Barrons.
The primary system of learning about and applying to British universities is through UCAS, found at www.ucas.com. Their guide books are tomes, available for borrowing in Student Services. For an interpretive guide, look to The Guardian University Guide, available in bookstores throughout the city. Another helpful website is www.hero.ac.uk.
Get the annual Maclean's magazine issue that describes and ranks colleges, usually published in November. Each province has its own system for applying and private universities are handled separately. The most comprehensive online resource is here: www.aucc.ca.
Virtually all colleges have their own websites. Start there for information about individual schools. There are several general sites that you may find useful: