We are going to need some kind of a budget to be really helpful. I've seen a $2600 two lens kit suggested in this thread already.
Assuming this is for a 1.6X body I suggest that the range above 100mm or so is likely to be the least critical. When I travel I seldom need anything beyond medium telephoto range. I'm going to give you a list of suggestions, I'l try to place them in order from cheapest to most expensive. Typically the cheapest ones are also going to be appealingly small and light for travel. I'm not recommending anything really onerous for travel like the 70-200/2.8 which (IMO) is too much for anything other than a photography dedicated trip.
There are a couple ways to go, depending on whether you like an ultra wide angle or not.
To start, if 17/18mm is wide enough for you then you might be fine with lenses like the Canon EF-S 18-55 IS, EF-S 17-85 IS, Sigma 17-70, Tamron 17-50 and Canon EF-S 17-55 IS (listed in order of increasing cost). The real budget and lightweight kit would have you take just one of the above lenses and nothing else.
If you really think you might want a telephoto then pair these with the Canon EF-S 55-250 IS, EF 70-300 IS or the 70-200/4 IS (in order of increasing cost).
The other path emphasizes wide over long, and gives maximum coverage in the range you are likely to want. The downside of this two lens kit approach is that it will have you changing lenses all the time as the break point between the lenses is in the heart of the wide range. Anyway, pair a Sigma 10-20 or Canon EF-S 10-22 with either the Canon 28-105 1:3.5-4.5, Canon 28-135IS or the Canon 24-105L IS.