As many of you know, I've been using the 5dMark2 pretty much since the camera came out in late 2008. Specifically, I've been shooting with the camera for a feature documentary and have since built up quite a kit of lenses. With so many lenses and manufacturers out there, it's hard to know which lenses to get and which work specifically for shooting docs.
Shooting with the camera on documentaries is tricky because you don't want to constantly be changing lenses, on the other hand the whole reason to use the camera is so that you can get that beautiful depth of field that we all love. It also important to use fast glass so that you're not spending hours lighting for interviews.
Having said that here are some recommendations for lenses to buy/rent if you plan to shoot a professional documentary with the camera.
*UPDATE: 1. Canon 16-35mm/2.8L Ever since I bought this lens a few months ago, it's been my go to lens for travel documentary segments i shoot for American Airlines. it's half the weight of the 24-70mm and it is a more useful range as you can get great landscape shots and great interior shots in small settings. also it's extreme wide is very forgiving when handheld. my last two shoots in costa rica and alaska i almost used this lens exclusively for handheld work and it was fantastic. The 24-70 never got used.
2. Canon 24-70mm/2.8L Still a very practical lens range. It's a bit heavier than i would like but it's versatile and fast.
3. Canon 70-200mm/2.8L IS. Very important to get the IS version of this lens. Probably the best zoom lens in this focal length ever made. This is my main lens for doing interviews on tripod. Just gives a beautiful depth of field and the zoom lets you vary shots. NOTE: Canon released a new v2 of this lens recently but I have not tested it (don't know if it's worth the extra $800 if you're using it primarily for HD video).
4. Zeiss 50mm/1.4. If you had to buy only one lens for the HDSLR package, I would buy this one. It gives and extraordinary bokeh and the movement of the glass if very smooth. I use this to shoot at night and for beauty shots. Extremely lightweight and it has a long rotation which is great for focusing or using a follow focus.
5. Canon 28mm/1.8 A great little fast lens for handheld stuff. I find this useful when i'm doing running and gunning, both at night and day because of it's weight. Great for doing low shots or if you know you'll be moving around an event for long periods of time.
Here are some other great lenses more for cinema look. These are lenses I would recommend and have shot with in more controlled narrative or studio settings.
6. Zeiss 85mm/1.4 or Canon 85mm/1.2 (great lenses again for cinema look) but not practical for doc work. Gorgeous lenses both of them. UPDATE: Just shot this lens on a commercial shoot. gorgeous!
7. Canon 24mm/1.4L Again a great fast wide L glass, but 3x as heavy as my suggested 28mm/1.8.
8. Canon 50mm/1.2L Again for the price I think the Zeiss lens is a bit more practical and in my opinion gives a more pleasing color rendition. But that extra stop makes for stunning shots and if you use autofocus it would help.
9. Lensbaby or T/S. These are great selective focus lenses. The lensbaby is the poor man's Tilt and Shift but gives an interesting image. Great for mood, music videos, commercials.
Don't be afraid to buy used glass. You can save a fortune and the great thing about lenses is that they keep their value over time. Going on craigslist is great, but I have to give a recommendation to Adorama because they offer a 3 year warranty on all their used glass. They have a surprisingly large amount of great lenses and their list is constantly changing. Also you can buy all kinds of old manual lenses from Nikon, Pentax, Minolta for really cheap and use an adapter.
Renting lenses is also very easy. If you're in NYC, Adorama, Calumet, K&M, Hello World, Tamberelli, Abelcine all rent lenses at surprisingly low prices. Also it's good to test a lens before you plunk down hundreds and sometimes thousands of dollars.
Use quality glass.... it makes a difference. I've tried going with cheaper glass like Sigma and Tamron. And I found that the lenses ended up staying in my bag. I've sold all of them and gone for Canon L glass and Zeiss.
So good luck and happy lensing....