I always find it amusing when I see photographers with cameras costing thousands of pounds using cheap consumer zooms. The rule has always been spend the money on the glass not the camera.
Now some consumer zooms are very very good. The Nikkor 70-300mm is a good case in point, while a consumer lens and built to a price, it does seem a little flimsy in its construction compared to the pro glass but for its price it produces excellent results. Sometimes having super zoom so you can react and get the shot instead of having to change lens can be an advantage.
I see comments on forums saying Canon glass is better then Nikon or Olympus is better then Panasonic. Judging a lens one must consider the design criteria. Sharpness and Contrast are what people want from modern lens, Canon and Nikon prioritise one of the other and each manufacture has picked differently so the look from the lens is different. Depending on which you prefer you might prefer one manufacture over the other.
Also how a lens treats contrast and sharpness can make it suitable for different purposes. Many portrait photographers like the look of older lens, they seem to blow and soften the highlights in an extremely pleasing way and while you can do it in post production there is a trend now to trying to get it right in camera again, and some of the great classic portrait lens can be purchased quite cheaply.
Its making use of old lens that has made micro four-thirds so popular. Adapters are available now for most of the lens available and with the crop factor of that format, the cameras are using the sweet centre spot of the lens.
When your talking exotic glass then people immediately think about the Leica Noctilux 50mm. Over the years this lens has gotten faster and faster with the latest version being now f/0.95. The other lens thats worth mentioning in the Leica world is the new 50mm Apo-Summicron M which is f/2. Now that does not sound like a special lens but this 50mm was designed to be as close to perfect and modern design could make it. No matter what aperture you use its close to perfect. Leica said a few years ago after they had designed this lens that they would not put it into production as no one would buy it. At nearly six thousand pounds for an 50mm f/2 you would be hard to justify it, but Leica changed their minds and put it into production and its selling like hot cakes.
The other exotics that people think about are the telephotos. The 600mm and 800mm monsters, used by sports and wildlife photographers. These lens have a fantasic price and a fantastic weight to match. If you can afford one, then you also need to budget a couple of thousand for a matching tripod and gimbal head.
While Nikon make some very big lens that are special order, the only off the shelf big telephoto until recently was the 600mm, but now they have a new 800mm which comes with a matched teleconverter to bring it up to 1000mm.
The wildlife and landscape photographer Moose Peterson recently posts a fun little YouTube video about this lens which you might want to check out. If your interested in this kind of lens then remember to be sat down when you read out the price ;).