Personally, I rarely see the point in overlapping focal lengths. If you've got the 18-55mm range covered, why by another lens that covers the same range unless it's
much better quality? Thats why I would go for a telephoto zoom rather than a super zoom.
If you've got up to £500 to spend then the best long lens you'll get for your money is the
Canon EF 70-300mm f/4-5.6 IS USM.
Of course, that requires you to have a Canon camera, which I think you do?
There are other options for these lenses, such as the Sigma ones and the Canon 55-250mm, but this one is pretty much the best one for Canon cameras that costs less than a grand.