I did not want something too heavy or too expensive while I was traveling, so no Canon 70-200mm F/2.8 IS II. But on the other hand, I did not want to degrade the quality of photos by buying something too cheap. For the first time, I decided to go with non-Canon lens for two main reasons. The first reason was because of cost. The Tamron lens was $150 less than the equivalent Canon. Secondly, even if auto-focus of the Tamron lens is not as fast as the Canon lens, the glass is of higher quality, image stabilization is more efficient (4 vs 2 stops for Canon), and the finish is much better (the Canon is from 2003 whereas the Tamron lens just came out in 2010).
When we arrived in the North Island of New Zealand, I added a new lens to my collection, a Tamron SP 70-300mm F4-5.6 Di VC USD.
My new Tamron lens:
Tamron AF 70-300mm f/4.0-5.6 SP Di VC USD XLD for Canon Digital SLR Cameras
The Canon equivalent:
Canon EF 70-300mm f/4-5.6 IS USM Lens for Canon EOS SLR Cameras