I use a plain old Jansport, it's at least seven, if not eight, years old. I think it's either the
Superbreak or the
Perfect Score, sometimes with a case for the laptop and sometimes without.
Case or no depends on how much else I have in the bag, and how heavy/full of sharp corners they are.
I also have a messenger (a Timbuk2, in the medium size), without a built-in laptop sleeve. One of the things I like about not having a built in laptop compartment is that there's no wasted space if I'm not carrying my laptop around.
Before I left for school, I definitely thought I would be carrying my laptop every day, and planned on also carrying around textbooks. I just graduated in May, and for the most part, neither my laptop nor my textbooks came to class, although my laptop came with me other places. Obviously, your experience might vary, I know people who carried their laptops everywhere, I know people who carried every textbook for every class with them.
I definitely got a lot of use out of my Jansport, so I can recommend those if you're just looking for something basic & flexible. The only thing that wasn't ideal was that the model I had was "water-resistant", a downpour could still manage to soak through the fabric, and things would get damp. Don't know if that's a concern for you, but I went to school in New Orleans unexpected showers were pretty common.
If you're looking for something a little more well-designed/engineered, I highly, highly recommend the bags Eagle Creek makes, especially the
Back Office, although you'll lose some space with the integrated laptop carrier. They're built really well, I use it as my primary "travel bag", since it'll fit underneath airplane seats and means I don't have to empty out my school bag everytime I flew.