I've always wanted a larger bottle than a standard baby bottle for drinking. They just don't hold that much for us larger babies. There are a few AB sites out there that offer specific adult-sized bottles, but now there are a number of simple solutions to the bottle size problem.
First there is an infant nipple adapter called Green Sprouts Water Bottle Cap that screws into most water bottles. If you search Amazon, you will find there are many other adapters for plastic water bottles including in toddler sizes. I have not tried any of these so I can't tell you how well they work. The good news is that it appears they will screw into common water bottles, which hold much more liquid than a normal baby bottle.
The other option is one I tried out today. Kleen Kanteen, a company that makes a variety of stainless steel drinking bottles, now sells an Avent adapter to use with Avent Sippy Spouts and it's bottles. Furthermore, I found out that the Avent adapters that screw my Kleen Kanteen will also work for my # 4 Avent bottle nipples. The result is I currently have a 40 oz. Bottle with BPA free attachments that make for either a huge sippy cup or a huge baby bottle. Now my only problem is I need to rest my arms after a long drink.