[RazorRain]

I found out this recently near the hill of Pike Creek you can climb on it and start shooting the cars below using a bazooka or guns till the explode to get some fast cash. Dont shoot the police cars or pedestrians which will cause the wanted level to go up high.

[Nukey Shay]

The problem with that location is that there are no nearby bribes or P/S garages to get to once the wanted level starts climbing (and it will). Virtually no advantage over targeting stuff from the SV garage or safehouse doorway...or even the Staunton carpark middle levels (so helicopter gunfire is not an issue).

On the subject of locations where you are virtually immune from the enemy, try standing under the water near the SV safehouse. Use the tunnel glitch to get there...the ground is solid below the water and the police will literally kill themselves trying to get at you

The easiest/quickest way to get lots of cash (without using a cheat code) is still probably "Vigilante". The game pause exploit means that you don't need to chase or shoot anyone once they are in view (just run them over). The side view exploit helps you to avoid being pulled out of the vehicle. So you'd only need to be concerned with enemy gunfire. Using a Rhino, you don't even need to be concerned with that.

[GTAFanLuca]

You can also bump your car with others, that make some cash too.

[thecommander]

Don't forget simply taking them to the crusher.

[Heihachi_73]

Line up 25-30 cars in the multi-storey car park in Newport, on the second highest rooftop level. When the top level runs out of cars, go down one level to spawn more vehicles back on the topmost level. If you go more than one level down, your newly parked cars may disappear. When you have a heap of cars bunched together, "accidentally" lose a grenade between all of the cars.

Hint: Avoid crappy cars like the Manana, Cabbie or Perennial since they don't offer many points when destroyed. Sports cars, and the Patriot, Bobcat and Rumpo all give better amounts. If you drove a car up to the top, it will vanish after grabbing a few cars, and I believe the game is limited to 32 cars maximum before it starts removing them from the screen. You'll know when you're reaching the vehicle limit because cars will stop spawning close to you and you'll have to walk half way across the roof to get to them. Every subsequent explosion increases the score multiplier, so if 4 cars worth 80 points each (dollars) blow up one after another, it adds 80 + 160 + 240 + 320.

Alternatively, just spawn cars using the import/export garage, assuming you have completed the lists (the one in Shoreside Vale could attract police however, especially if pedestrians with an IQ of -1 decide to start walking between exploding cars).

[7DZ]

My methods (no cheats used):
For PS2/XBox: start Vigilante, when being near threat(s) pause the game, go back to the game, once they exit run them over. Requires a lot of time, patience and the best time to do this is at the beginning in Portland when no gangs hate you.
For PC: start Firefighter, press F1 (replay), press F1 to go back to the game and voila - game thinks that fire is extinguished. Way, way, way faster then method with vigilante. I remember I managed to get about 360.000.000 $ with this, then gave up.

[gtaIII48]

I read this on ign get 2 tanks using GIVEUSATANK and keep hitting one with the other