Yep, any Micro 4/3 lens will work. Additionally, any 4/3 lens with an adapter. Also (with adapter), just about any Leica (R, M, L39), Olympus (OM, Pen F), Nikon (F, G, S), Pentax (K, 110, M42), Contax (C/Y, G, RF), Minolta, PL, Praktica B, Exakta, Canon FD, and quite a few C-mount lenses.
If you have no idea what you want, start with a modestly-priced slow wide-range zoom (Lumix 14-42, 14-45, or 14-140) and see what ranges you really tend to use most, and where you need more speed... then refine from there.
No one lens will do everything, and if it did, there'd be no point in owning an interchangeable lens camera.
the major problem with m4/3 is there arent many really good looking native lenses.
i had the most luck with adapted old nikon primes. but of course when you adapt a lens you lose all modern features like OIS or AF...
one of the best, native m4/3, multipurpose lenses you'll find is the panasonic 12-35 2.8. but its upward of $1200
That's subjective, of course. I think my m43 P7-14/4, PL25/1.4, CV17.5/0.95 are all excellent glass (not really cheap, though). Used to own and enjoy the 20/1.7 and 100-300 as well, but sold them on a cost-per-actual useage and overlap equation. I've seen plenty of good material from the cheaper alternatives as well.
Lumix lenses tend to be very sharp and contrasty. Some people don't like sharp and contrasty, just as some people don't like that vintage low-contrast look.
Keep in mind that the GH3 body is weather sealed but not many m43 lenses are. So if you plan on shooting in wet, snowy, or dusty environments you might want a weather sealed lens.
No way I'll be able to afford any of the new gh3 lenses after buying the gh3 so I'm thinking I'll use the gh2 14-42mm on the gh3 and put my 45-200mm gh2 lens on the gh2.
That configuration will have to stand me for a while.