I'm going to buy myself a more powerful zoom lens in the near future. I was hoping that some of you wonderful photographers out there may be able to help me out a little and give me your suggestions?

I have totaly fallen in love with macro-photography, and think I want to focus more on close-up shots than landscapes and what have you. What is a good 200+ lens?

The camera in question is a Cannon 350D, and it is usually equipped with the Tamron 55-200 lens.

I thank anyone who is kind enough to take the time and respond - I will be in your debt. Thanks again!