For those who keep to it, the main constraint is the 2-'L' limit more than the 4 lens total limit - though I see that that is too challenging for some! ;-)
So, to free up an 'L' slot, I'd think about the new 70-300 IS.
For a 1.6 crop, the 10-22 EFS is obvious, and, again, doesn't take up an 'L' slot.
I'm tempted by a 35L, 135L combination, but that leaves big gaps between 22 and 70.
So, assuming someone else is paying(!), I'd end up with:
10-22, 24-70L, 70-300 IS, 200/1.8L,
the logic being that at the long end, you get a zoom with flexibility and IS, but limited aperture, complemented by a prime with less flexibility, no IS, but a great big aperture.
