I definitely concur with Daniel and Rich - while I think the 18-200mm is a decent lens, any superzoom lens like that mean a lot of compromise in terms of distortion and other issues. Since you already have the 18-55mm lens (decent, especially at narrower apertures), adding the Canon 70-200mm f/4L would be a good choice, and slightly cheaper than the 18-200mm. The 70-200mm f/4L is an L-series lens - excellent quality!