Hmmm I missed this whole thread. I think the 5D2 and 24-105mm combo would work. 24mm is adequate on a full frame for most landscape shots (even though I also own the 17-40mm). If you feel like you want something a little longer then the Canon 70-200mm f/4L IS is a fantastic travel lens as well.

When we travelled through Vietnam and Cambodia two years ago I had my Canon 40D, Canon 28-135mm f/3.5-5.6 and Canon 50mm f/1.8 II. So a pretty basic, low end kit really. I still managed to get some fantastic shots, and they'll always be great shots because they'll spark a few memories of our trip.

On another note, if you're heading to Siem Reap in Cambodia be sure to check out Tonle Sap - it's a huge freshwater lake and everyone lives on the water. I really enjoyed it, obviously head to Angkor Wat etc because it's just an amazing place. In Vietnam - don't miss Hoi An and Halong Bay, both essential destinations. Halong Bay is serioulsy spectacular.