My munchkin did the same thing. He's 5 now and a little small for his age, I think because he didn't eat anything for almost a year and he had a spit-up problem.
The doctor told me that I had to give him no choice but the sippy cup, and that he would eventually take it rather than go thirsty. The doc also said that kids don't drink as much from a sippy cup, which would cause him to be hungry and eat solid foods.
I thought that sounded awfully cruel because my son loved his bottle so much and it seemed to be a great comfort and security to him. I put it off for about a month, but when he turned 1 and still wasn't eating I gave it a try. It was really hard for both of us but sure enough, the doc was right. He threw fits and didn't drink much for a few days (he drank enough to stay healthy) and I felt like the biggest meanie alive, but over a few weeks it became the new routine. The doc also said that I had to realize that the amount of liquid he was drinking was much higher than his daily requirements, and not to be alarmed if the liquid volume consumed went down with sippy cup use. You should ask your doctor exactly how much liquid he really NEEDS a day instead of wants and make sure he gets that much during the transition time.
I did cheat every once in a while when we had to go on an outing and I knew he would be an unstable wreck without his bottle. He got a small bottle then, but now that I look back, those little cheatings did nothing much more than set him back and make him want his bottle.
Hope that helps, or at least makes you feel like you're not the only one.
Oh, and i guess my main point here is that the problem was that he was filling up on formula or milk because he just loved his bottle so much. I tried the millions of different tasty foods thing, but that was not solving the problem because the comfort of his bottle gave him more pleasure than the delicious taste of any food - even fruits and chocolate. So, I had to eliminate the real appetite killer first. Then, he started eating a variety of foods and even liked things that most kids didn't. He wasn't picky - he just wasn't hungry.