EDIT: lol holy cow, a lot of people are referencing this particular blog post lately (most recently from conceptart's Sheridan topic). I just wanted to give a few tips and warnings;
This portfolio was mainly geared towards Animation. It received a score of 3.77 out of 4 (minimum score of admission last year was 2.99+). I mainly concentrated on skeleton studies and gesture life drawings, nothing else, no detailed painting or fancy things like that which would have been necessary for Illustration.
Because of that, I've gotten a much better score compared to my Illustration portfolio, which received a decent-but-not-stellar score (70/100, minimum score of admission last year was 59+).
So uh... For those who're aiming for Animation, if you can do a lot of good research/sketchbook pages, skeleton/muscle studies, perspective studies, and decent life & animal drawings, you'll do more than fine.
For Illustration, however, I haven't researched the best ways to get into the program so I can't help as much... I've seen a lot of good portfolios that carried paintings, still lives and experimental illustration-y stuff. Although, I'd aim to get good draftsmanship more than anything else.
I think the most important thing to consider while making a portfolio is to show the school that you have potential to learn. You gotta be willing to show them that "yeah, I don't know much anatomy or perspective anything, but studying it interests me!" that's why my animation portfolio got in really well; sketchbook studies and skeleton and muscle and all that stuff shows the instructors that YOU WANT TO GET IN THE PROGRAM IN ORDER TO LEARN THIS STUFF.
Here are some of the stuff I've submitted for my Illustration and Animation portfolios in Sheridan.
Most of these were done last minute, like... probably during the last week before the portfolio due dates. Don't try this at home, kids.