Lens advice: 24-105L vs. 70-200 F4L

Hi. I'm looking to get a 50D very soon, but am conflicted (read: know very little) about which lens(es) to get. I love nature and travel photography (landscapes, people, architecture, etc), and am deliberating between a couple different lenses.

I'm considering getting the 24-105L, which sounds like a fantastic everyday lens. But, that may not leave me with enough zoom to get some farther away shots. Thus, I'm also considering a combo of the 70-200 f4L and the 18-55IS. I realize there's a big difference in lens quality with that last combo, but it's within my budget (I'm trying to stay under $2500 for the body and lenses). I guess I could always get an extender for the 24-105L, but would that provide enough? The choices I've laid out are roughly the same cost.

Thanks very much!