There is also a fantatic mod thats been out a while called RealGTA - re-maps all cars and even adds new areas into the GTA 3 map. Includes such cars as the new Porsche and the Viper GTS-R.
Not for slow machines though, as the models are so well detailed that they suck the computer dry. I'll post pictures if anyone's interested, but the game is aging a bit now so I am not sure anyone would be. I'll have to re-install the game, it's been a while!
Here is the picture that came with it's release, just shows more terrain, no vehicles.
Also, there is a multiplayer version of Vice City called Multi Theft Auto - its fairly ok, and can be played online over dialup, but there are no pedestrians (only human players in a death match) and only limited set vehicles around the city. Also, the Apache is in but does no damage (unfair advantage apparently).
And how good were the originals? The very first one had me hooked, right from the start. Good ol look down views, hijacking trains, running over as many Hari Krishna (spelling?) people as possible, the Elvis has left the Building score!!!