While I was in New York I hired a fisheye lens for my camera. I got a special offer because it was Labor Day, or Yom Kippur, or both...I don't remember. Either way, I got 5 days for the price of 1, so it was a good start.
I [heart] fisheye.
Honestly, for urban photography, it's amazing! You can really concentrate on your foreground but keep the background visible. You can take a photograph that shows the view down two streets that are at right angles to each other! You can get close-ups of strangers without them realising that you're taking their picture! More than anything though, the wide, wide angle lets you fit more picture into the same space. I no longer had to choose to show people or buildings, I could show both, and do them justice! I could take much wider cityscapes (which are more interesting than general panoramic shots in my opinion). I had SO MUCH FUN with the fisheye lens!
That's probably enough words, here's a couple of shots: