A co-worker asked me today what would help him minimize the amount of lenses he needs to carry around during his travels. Although I'm a big fan of Canon products, I think Tamron has this area on lock. Personally on my travels, i’m carrying around the Tamron 18-270mm Di II (this is a newer version not to be mistaken with the older version). It mounts on the Canon 5D Mark II as an EF mount, auto-focus works, but you'll get crazy Vignette on that full frame. This lens will only work properly on cropped cameras. It also can't maintain an aperture throughout, and ends up at F/6.3, but the IS they have will help in slow shutter speeds. Something I don't worry too much about since these cameras are fairly clean with High ISO.
If you want to see a sample Video, the Video below was shot mainly with my Tamron 18-270mm. That's correct, the actual lens that's in my bag was on loan to my buddy Roland as he wandered around China.
Not the sharpest lens in the bag, but hey the Image Stabilization works wonders for both Photo and Video, and runs you only over $620.00 bucks. You can't complain about that type of range for that type of price. This is the Tamron 18-270 Di II lens that i'm using on my Canon 7D.
Below are examples I took while at the Academy of Sciences in Golden Gate park. First shot is wide (there's a butterfly somewhere in the middle) and the second shot is zoomed in at 270mm handheld with their IS on. Click the images for the large version.