I personally like and use a Canon EF 50mm F/1.8 II. For its price of 125$ (On Amazon), it is very, very powerful. It has got spectacular optics, better than most other Canon lenses. It is very lightweight. Can be used as a normal lens for full-frame digital film and a short tele for 1.6x cameras. It works very well in low-light situations. The downsides of the lens is that manual focus requires moving a switch, and the focus ring turns as the lens autofocuses. Since it uses a plastic mount, this lens will break very easily. Treat the lens with respect, though. In my opinion it preforms better than the 2200$ 14mm F/2.8 L II.
I own a Nikon D600 DSLR. I have bought Nikon AF-S Nikkor 28mm f/1.8G which is a wide angle lens, to use with my DSLR. It was fairly inexpensive. The focus is fast and it is super sharp.
I don't own any DSLR, but I can talk from my phone experience. Carl Zeiss, which is usually implemented on Nokia phone, is truly neat and you can definitely see the difference compared with other phones that fall in the same category of price. But again, I'm no savvy...
