I use a lot of binders at work...

...and will use whatever we have lying around the office - the basic white ones. But, I was in OfficeMax a few weeks ago and picked up a few new Avery binders. Apparently the Heavy-Duty Reference EZD View Binders are great because they have multiple pockets, a back mounted ring so the pages lie flat and you can open or close the ring with one hand. Personally, I just like the cool colors (green, pink, or purple) and the jealous looks I get from my colleagues...