Can you recommend your favorite sites for purchasing college textbooks?

I just found out what books I need for my first semester classes, so I’m going through the process of finding the best deals. I would rather not rent books as I would like to have the option to write/highlight in them, and it seems that renting is almost as expensive as just buying the books in many cases. New is obviously ideal, but I’m certainly open to used books that are in good condition if the price difference is significant.

Do you have any favorite sites where you bought or currently buy your books? Any other advice on the topic is also greatly appreciated.