You can't beat the fast primes for sharpness, bokeh and selective focus. Some of the ones people have mentioned are less expensive than the fast zooms too. You mentioned buying lights, so I assume you're looking to do posed portraits. In that case, you won't really need the variable focal length as much anyway.
On the other hand, if you want to shoot candids, then the zooms will really be handy. But I end up shooting candids at focal lengths longer than 80 almost all of the time, so I don't think the 24-70 would be my first choice. Great for landscapes though.
That leaves the 70-200s. As others have said, the 70-200 2.8 is really intended for use wide open. If you don't need f2.8 (which is really useful for blurring backgrounds), go for the f4. The f2.8 is pretty big and heavy. When I was younger, I didn't care. Now I'm finding I can't handhold lenses that big as steadily as I used to.
I'm about to buy a 24-105 L. I'm thinking that could become my go-to candid portrait lens in the field. But again, for posed portraits, I'd get a really great prime lens, like an 85. If you have nothing else in that focal length range now, you might even consider something like Sigma's 105 macro lens. Extremely sharp, insignificant distortion, (relatively) cheap, and useful for other purposes.