Upload & Sell: On
To add some more clarification...the following are companies that make Mirrorless System Cameras (sometimes called MILC for Mirrorless Interchangeable Lens Camera...sometimes called CSC for Compact System Camera.....there's more acronyms too like EVIL or DSLM...noone has settled on a specific acronym for these cameras, but they're not DSLRs because they don't have the mirror that the Reflex portion of DSLR refers to).
Panasonic: Micro 4/3
Olympus: Micro 4/3
Sony: E-Mount (NEX)
Canon: EM Mount (EOS M)
Nikon: 1 (or CX format)
Fuji: X Mount
Pentax: Q mount
These companies also make lenses for their mirrorless cams, but third parties also make lenses for these cameras, though mostly for Micro 4/3 and Sony NEX (E-mount)
Sigma makes them for both m4/3 and NEX, Zeiss makes them for NEX. Voigtlander, Schneider, Samyang, and a few smaller companies also make them for Micro 4/3. Tamron makes them for NEX and may eventually do some m4/3 lenses. Leica designs lenses that are then produced by Panasonic and carry the Leica name...for micro 4/3, of course.
I haven't seen third party lenses for the other mounts yet, but I'm sure they'll come as they gain popularity. Right now, Micro 4/3 and NEX are the big ones in the mirrorless segment.