Here are four styles of NYC taxicabs.
Some have roof billboards, some have bumper-guards, one has a digital billboard, one has body-colored bumpers.
They are all modeled after New York City's newest Ford Crown Victoria (model years 2000-2003) taxicabs. Here in Manhattan, the newest taxis are entirely yellow, while other older ones have grey bumpers and black stripes along the doors. They all have a green "badge" on their hoods. You'll also see a spattering of cabs with advertisments on their roofs, the newest of which are digital signs that change with updates from satellites!
Also check out my large scale taxi and my tiny scale taxi
Here is a picture of all 4 of my taxis, detailing out all the subtle differences between the models.
This taxi has one of the new "electronic" billboards on the roof. In real life, these billboards light up and show everything from animated advertisements to up-to-the minute sports scores from satellite uplinks.
Here is a newer taxi cab (2002 or 2003 model year), with a roof billboard, and body-color bumpers. These newer taxi cabs no longer have grey bumpers or bumper guards, and they have black plastic grilles instead of chrome ones.
Here is the "standard" NYC taxicab. You can see the bumperguards on the front and back, the grey bumpers, and the black stripe down the middle.
This picture also shows off the angle that I usually build my cars on. I think it helps make the cars look more modern, since modern cars usually have higher trunks and sloping door lines.