I shoot mostly video with my 5DII but some stills. Probably my most used lens is the Zeiss 50 f1.4. Then I use my old Nikkors with adapters, including the 24, 35, 105 and 50 micro. For shooting interviews I have the Canon 70-200 F4. I got that one over the f2.8 because it's lighter in weight and doesn't need a lens support for tripod use.
Most of what I do is under controlled situations so using primes is fine. But I also do quite a bit of run-'n-gun documentary type things, and while switching out lenses is quick, switching out ND filters adds to the time. I have to take off the lens, put the next lens on, take one or more ND filters off the first lens and put them on the second lens. I use all 77mm filters with stepdown rings, so I don't have to worry about different thread sizes. Most people use a mattebox and 4x4 filters, but to me that adds weight and bulk.
So, because of the doc-style work I do, my next lens will be the 24-105. I started to buy it with the camera for that kit price but didn't. Now I wish I had. It's a great lens if you want to just go out with a single lens. And for a zoom it's nice and sharp and has that great Canon color, much like my ancient Nikkors. For my work, I rarely open up beyond an f4 anyway, unless I really need to blur the background so much that you can't tell what's there. The DOF of the 5D is so shallow that generally I shoot at a 5.6. I think that for most of what I do I could live with the 24-105 and the 50 f1.4 for situations where I need a bigger aperture.
That's a long winded response, but the point is--what type of work are you doing for the most part? That will determine the best lenses for you. If all i did was location documentary style things, the 24-105 and the 70-200 would be all I'd need. For studio work, dolly shots, Steadicam work, etc., I prefer using primes.