[N54YO]

I use the 28-70 F2.8 L. It's the older model of the 24-70 but its still great. Next up would be the 70-200 IS 2.8 L. With those 2 lens, you should be good. Or Canon just released the 18-200 IS F3.5 I think. Take a look at that if you want a good walk around lens.