The 70-200 is a great lens, esp outdoors where space is not an issue. For low light indoor ambients, I like the 35L; it's more forgiving than the 50L. A lot of people will recommend the 24-105, but I don't think it's as useful if you intend on getting more lenses and the new 24-70 II looks to be a great performer (albeit a very costly one, at least initially). For general travel, I like the 16-35, 50, 70-200 combo which gives you a large focal length range and low light capability.