Whatever fits your exact budge I guess would be the best place to start.

Do you want a zoom or prime? Aperture control? Are you willing to buy an adapter to allow other lenses other than m4/3 to work with it?

I personally am a fan of Rokinon (35/85mm t1.5) lenses because they are affordable with pretty nice results, and if you was to drop or get stolen, you wouldn't be as suicidal as if it was a $3000 lens lol. Another affordable lens that I find gives a descent image is the Sigma 30mm 1.4 with a Variable ND filter. Both lenses I mentioned would require a m4/3 to canon adapter. Voightlander will also be highly suggested but then you are getting up in the $1000 range. As far as zoom lenses, somebody else will have to share advice, I'm having a hard time deciding on one myself right now.

Some will tell you that it doesn't matter what lens you use and it's more about how well you use the tools that you have. Although it's not a wrong answer, it's not the kind of answer you are expecting. If you REALLY are very new to this, just ease your way into it VS spending thousands of dollars to find out this isn't something you really want to do. The more you use the GH2 and get familiar with it, more than likely you will stay interested, and in no time, you will be able to charge people for your work, no 30 years experience necessary. Special thanks to Mr. Gates and Mr. Jobs and those that helped them along the way ; ) Modern technology and the blessings it provides for one to just "out of nowhere" decide to start making videos.

To learn filmmaking, I'd get a Canon FD 35mm f/2.0 with an adaptor and use that for just about everything. Then you can spend your time learning about filmmaking and not worrying too much about the lens.

I can recommend the canon fd 35mm f2.0 aswell. Its a very nice allround lens. Fast enough, still wide enough for most stuff, you can aswell try the canon fd 20mm f/2.8 which is a bit wider, but not as fast and kinda soft wide open. So the 35mm lens that douglashorn suggested is certainly a very good grab. The SSC version has a slightly warmer look, but also a slightly radioactive coating. People say its not an issue at all, but decide for yourself. The lens is certainly about the best buys and as good as you can get for that amount of money. You might also look at the Minoltas, they are excellent aswell and slightly cheaper.

Canon and Nikon lenses are not cheap. Minolta Rokkor lenses are excellent but much cheaper. You can find on ebay Rokkors 28mm f/2.8 and 50mm f/1.7 together for $60.

Our p-v mate nomad has written great article about vintage Minolta lenses recently, check here: http://www.personal-view.com/faqs/camera-usage/minolta-rokkor-lenses-faq

i have bought the rokinon series cinema lens exept for the 8mm. They are grate for the price, performance is incredible, and about the breathing, its ok.

New glass design is better then old one like nikon AI-S or canon FD. If you want carachter, then choose old lenses, or proper cinema lens. YOu want performance choose rokinon, then on post make it shine.