Mine are capable of using an open cup (have been for over a year!) However, once they take a few sips they tend to make a mess dumping it out, dipping their hands in, etc. so we usually only do water, and just a tiny bit. They will take most sippy or sport top bottles with silicone spouts. They can do cups with regular straws (like the take and toss ones) but they HATE straw sippies.
I am so embarrassed reading this thread! I am mortified to say they turned two in March and still get a nighttime bottle. Once their molars finally finish coming through I am planning on weaning them off. We have just had such terrible sleepers. I am enjoying FINALLY having them go to sleep in their beds and sleep through the night. I just can't deal with changing it up until I have a little more sleep again.