Money makes the world go round, and boy howdy, can you nab a ton of cash in Grand Theft Auto V...if you're willing to play dirty, that is. Such is the nature of exploits.
Here we have a video of SomeFilthyCasuals walking us through how to do a money exploit—it requires going to a specific place on the map, and switching between characters such that a suitcase respawns under you. If done over and over again, you can gain over a million dollars in an hour, according to our estimates—we tested it out, and sure enough, as of this writing, the exploit works. Note that you don't have to fret about making sure you switch characters right away, since it doesn't take long to recenter a character that drifts away from the suitcase.
Now the only question is: just what will you spend all that dough on?
GTA V: Infinite / Unlimited Money (Tutorial) [SomeFilthyCasuals]