One more thing to consider - you're paying for 18-200mm, but you're not getting 18-200mm. On a lark, I tried out an EF-S 18-200mm in a camera shop, and compared it to my EF-S 17-55mm and EF 70-200mm f/2.8L IS II. On the wide end, the framing at 18mm on the superzoom and approximately 18mm on my 17-55mm was equivalent. However, comparing the 18-200mm with the 70-200mm at 200mm, the L lens was noticeably longer. When I got home, I compared the shots and measured the framing with the two lenses, and the effective focal length of the 18-200mm at the long end was only 154mm compared to the 70-200mm (which I assume is delivering a real 200mm focal length).
So, compare the 18-200mm, which is really an 18-154mm, to the EF-S 18-135mm (which really delivers it's promised focal length). The former is a lot more expensive, but optically only slightly better than the 18-135, which offers nearly as much actual zoom.
However, in all honesty I'd recommend neither of them. I'd second Flake's recommendation of the EF-S 15-85mm f/3.5-5.6 IS - optically, it's much better than either of the other two. Personally, I actually prefer the EF-S 17-55mm f/2.8 IS because of its constant and fast aperture, but the 15-85mm is less expensive, wider and longer, and ideal as an outdoor walkaround lens.