K.,
I agree with the other prior posts. We used the Nuby soft topped "sippy cups". It's kind of between a sippy and "nipple" bottle. This worked until we did move to open cups.
The only reason we didn't go RIGHT to open cups is simply the mess.
I've heard other people who used the straw cups with success too. They have "disposable" ones - I think Playtex sells them, at Wal-Mart or the grocery store. they are primary colors and small, inexpensive cups. CostCo also sells the soft-straw sippys in sets of 4.
A final word of advice, if you are set on getting rid of the bottle, especially before bed, beware of a fight. You may have it established as a "habit" now. He may expect that to fall asleep before bed. Also, our dentist warned against this since the milk sits on their baby teeth all night. Maybe water before bed or make sure to brush his little teeth.
Stick with it. If you "give all the bottles away", then only offer milk in the sippy. When he wants it bad enough, he'll take it. (If he sees the bottles, he'll want them. Don't be fooled, he probably knows what cabinet or drawer you keep them in.)
Good luck.