Should I upgrade to 5D Mark II, or buy better lens for 7D?

I would have to agree with some of the other recommendations here, especially if you have EF-S lenses.

The EF-S lens line and other Non Mfg lenses with the digital designations are designed for, and will only work with cropped aps-c sensors, like the 7D, rather than the full frames cameras like the 5D Mark II. Upgrading your lenses to full frame compatible over time will benefit you long-term. However, if you have the budget and the Canon lenses that are already compatible with a full frame body, then I would definitely go with the 5D Mark II, as image quality is clearly outstanding. If you are looking for lenses, and are on a tighter budget, I would also check out refurbished lenses on the Canon direct store. They also have a selection of refurbished bodies including the Mark II from time to time.

subCategory_10051_10051_-1_22751 at shop.usa.canon.com

Hope this helps.

I would wait... Canon is announcing more cameras soon, and something like the rumored full frame 6D may be a better option for you. 

I own the 7D and I am keeping it because it has higher resolution and better auto focus.  I am buying the 5D Mark II because it is full frame and it does wonders with Magic Lantern 3.2 because it can do a lot more than what the stock firmware could do but it only works for 5D Mark II, 60D, 50D, T1, T2i, and T3i. Check out the link (http://www.magiclantern.fm/releasenotes) It wont work on 7D because it is carry dual processors (Dual DIGIC 4) this is why it is faster APS-C Canon ever made.  Canon EOS-1D Mark IV and Canon EOS X are more faster but more expensive.

However 7D will get newly firmware update 2.x.x with new features.  http://www.usa.canon.com/cusa/consumer/standard_display/EOS7D_firmware 7D is still great fast camera.

Buy some better lenses. and wait for the new full frame dslr from canon. i'd recomend the 24-70mm f/2.8L and 50mm f/1.2L.

And do not buy ane EF-S lenses if you plan to upgrade to fullframe.

7D is a way more modern camera then the 5DmkII. You can't compare the fullframe sensor x the cropped sensor, but you can compare : better autofocus, more focus points, more clicks per second, lighter, built in flash. You should invest on lenses, because the one that comes with the kit sucks. get EF lenses so when you upgrade you can use them on a full frame sensor camera. Stick with it and wait for a - maybe - 6D, or raise money and get the 5Dmk III. 

I would recommend it. Until you actually compare and can see the difference you will never know. Reading all the reviews online about DX or FX just confuses you. If you want sharp usable images at 3200-6400 ISO go full frame. I still own my DX body because it works great with zoom lenses. Worse case scenario is if you do not like FX sell it. You will get your money back. Better yet, rent an FX body and shoot all weekend with one. That should help you make your decision.

I suggest, buy some lenses... thats enough. Remember when you buy the Mark II you must buy lenses for that, too.