I have the Sorrento Carry You cup holder for my son. If you google it you will find many places that carry it. It works great. It attaches with velcro and has never fallen off. I tried many different cup holders before getting this one. This is by far the best one.
I also have the MacLaren universal organizer for the back of the stroller. I either got it from the MacLaren website or e-bay, I don't remember. It has a big mesh pocket to hold things, which comes in handy. It has two cup holders also. It works fine if you have drinks in bottles - soda, water, etc, but not so great if you have a cup with a lid on it. The drink tends to leak as you walk.