I have one outstanding sleeper lens. It's a Sigma Super Wide II f/2.8 24mm lens with a Nikon AIs mount. Uses 52mm filters, runs through to f22 and has half stop click stops, something no Nikkor lens does, as far as I know anyway.
The quality, whilst not equal too or better than Nikkor lenses, is nonetheless, extremely good to very very good. I actually bought this lens duty free just prior to leaving Australia, with the idea to use it on a European holiday then flog it when I got back home. The lens was so good I couldn't contemplate moving it along, plus, it was cheap as anything compared to anything Nikon, but more expensive than comparable after market manufacturers like Tamron.
Mick.