Several brands of baby bottles can be converted to toddler sippy cups.
Providing with the following benefits:
Lifefactory: Both the 4oz and 9oz Lifefactory glass baby bottles can now be converted to sippy cups with Lifefactory Sippy Converter Caps. With Lifefactory you also have the added convenience of being able to purchase just the 9 oz. bottle (with cap), just the sippy caps or the complete Lifefactory Sippy Cup Bottle, all of which are available here.
Pura: Pura offers a great stainless steel bottle where no plastic parts come into contact with your child's food. Pura bottles come in 5oz or 11oz sizes. Any Pura bottle can double as a baby bottle or sippy cup and will work with all of the following: