The problem we found with getting a baby to switch to a bottle is two things.
1. The flow of the milk is different.
2. The nipples texture is very different.
We found some silicone nipples that are supposed to be more realistic and have a flow rating. If you ask me, the texture is still way off, but the flow rating really helped. We had one kid who got lazy with one of the easier flows and didn't want to go back to breastfeeding. So try to get one with a similar flow rating to your own flow, unless you are trying to ween off the breast.
I've found them at Toys R'Us, and online with Amazon. I don't remember manufacturer or name of the product, but they said right in the description what their flow is and that they were supposed to be natural feeling.