I think Sigma makes an 18-250 which might be exactly what you're looking for.
Amazon.com: Sigma 18-250mm f/3.5-6.3 DC OS HSM IF Lens for Canon Digital SLR Cameras: Electronics
...and they have a popular 18-200 too:
Amazon.com: Sigma 18-200mm f/3.5-6.3 DC AF OS (Optical Stabilizer) Zoom Lens for Canon Digital SLR Cameras: Electronics
I have a Nikon D60 with an 18-55 and experience with a Nikon 70-300. I've been looking at getting one of these Sigma lenses based purely on amazon reviews and price. The 18-200 is $399 where the equivalent Nikon lens is close to $900. Seems like they're a good value for a lens you just want to carry around town with you.