Sony E-mount Adapters
Sony E-mount adapters come by the bucket, from cleanskin brands to the likes of K&F concept, Viltrox, Fotga, Fotodiox, Metabones and Commlite.
For manual focus lenses the cheaper options like K&F concept seem to do an excellent job, I use these in FD, M42, M39 and Pentax K - Nex. One problem you may encounter with cheaper adapters is the tolerance allowed during the manufacturing process, this can cause the lens to have issues reaching infinity. E-mount lenses have a FFL of 18mm while M42 lenses have a FFL of 45.46mm, this means that the adapter has to fill the space thats left, giving a distance of 27.46mm. If the adapter is 1mm or so longer then it should be you could simply sand or shave the face of the adapter away (evenly) until it's back to 27.46mm (I've done this with a fotga adapter). Not all cheaper adapters do this but sometimes you may find one that will.
For auto-focus lenses like EF - Nex system cameras. Fotodiox and Viltrox are worthy options with the Metabones being the most expensive brand, Once again depending on your budget and needs.
Once you start getting into the FFL of older (and newer) systems, the range of adaptable lenses seems to skyrocket.
For a list of Vintage 35mm Film adaptable lenses click Here
For a list of modern Full Frame lenses click here
It's important to note that E-mount system camera's have a FFL of 18mm, so any lens mount system that has a larger FFL can be adapted, provided the adapter is in production.
When attaching an adapter to your Sony E-mount camera it is important to select Menu > Settings > Release w/o lens to be able to use your manual lens. If this isn't selected your camera will still try to locate a lens attached and will not work.
When dealing with lenses like the Leica R, Zeiss and canon EF mount lenses that come equipped with Focus - confirm chips, this feature is not compatible with Sony A7 camera's. Which I personally would like to see available since focus peaking isn't very reliable. Focus magnification located on the C1 button is my first choice.
As you can see from this short list below plus many more that I have not identified there is a mass of lens options if you would like to try adapting.
Lens Mount FFL
Leica M mount - 27.8mm
Leica R - 47mm
Nikon F - 46.5mm
Canon FD - 42mm Canon FL - 42mm
Canon EF - 44mm
M39 - 28.8mm (earlier M39's Jupiter 8, Industar 55)
M42 - 45.46mm
Pentax K - 45.46mm
Contax G - 29mm
Yashica MA - 45.8mm
Minolta SR - 43.5mm
Konica F - 40.5mm
Konica AR - 40.5mm
Jupiter 8 with M39 adapter
Silver Helios 44-2 with M42 adapter