The 16 is very worthwhile as stated above.
I went over the top and bought this in alpha mount for the nex
the sigma 8-16mm designed for APS-C, about 650USD
I know, I know, it's huge, but the nex controls aperture via LAEA-1 and focus is not such a huge issue with something this wide.
Personally I have no problem with big lenses on the nex if I am hunting something special, otherwise I go into RF mode with the 16, M and LTM glass.
BTW, there is some thought that "legacy glass" cannot resolve on modern sensors. This sigma has quite good reviews, and I find it just fine, but I have a number of legacy lenses which out reslove it easily, e.g.: nFD 20 F/2.8, nFD 24 f/2 (far better than Nikon 24 2), Nikon 28 F/2 AI, Nikon 55 micro AIS (incredibly sharp all the way out--I think it can hold it's own against almost anything), Bokina, Kiron 105, Nikon 135 f/2.8 AIS, and Nikon 180 AIS ED, all have very very high resolution on the nex aps-c, superior to all e-mounts, including 18-200, the best of them, which I also have. No, I'm not rich, just obsessed.
Now, I admit the 35mm sony SAM "easy choice" f/1.8 CAN keep up with those old dogs, but it may as well be MF, and does not offer live aperture view in the nex.
The trick is to pick your legacy glass carefully. Sure there are some modern primes, and some really high-end zooms which will beat nearly any legacy lens, but they cost thousands. A 55 micro goes for 75USD. All the Primes above can be had, with patience, for less than 250USD.
By any measure, one of the great 24mms of all time.
ref:
http://home.comcast.net/~starka/24mm/24mmIntro.htm
"Based on my own findings and results from a couple of independent websites and people who have tested these lenses I can comfortably say that the nFD 24mm f2.0 is probably the best lens of the Canon FD series"
i.e. the best FD mount lens ever made.
I found this one, like new, in Austria for 250USD+20 shipping to USA.
With FD adapter it is about 8mm longer than the 18-55 kit collapsed, but 12mm shorter than the kit extended, with a nearly identical diameter. It's heavier, but that's partly due to the fact we don't yet have ultra light adpaters.
Trivia: what sharp, fast, normal prime, is smaller than the kit zoom with adapter by alot, and can be had for less than 50USD?