I've read a lot about how people have become bored with the game and blah blah blah. (insert whine here)
I myself have not become bored with the game, but for those who have, might want to try this....
When Trevor and Michael are exiled from the city, Madrazo's men come at you non-stop. You can use this point in the game for some non-stop high-octane action!
When you get to the point where you are exiled from the city, make a separate save game. This can be used as a "Fun" save when you can use cheats and what not plus you have an endless supply of targets which makes testing out those cheats even more fun!
Madrazo's men come at you relentlessly, I have driven into police stations and watched as the police shoot it out with Madrazo's men. If you shoot back, the police will target you so watch out! Madrazo's men will retreat after a long while when the police call in backup. It's hilarious to see them run off.
The same actually works in Ballas and other gang territory. If you hide behind some Ballas while they are chasing you, the gangs will shoot back and call in reinforcements. This also works if you manage to find some Lost on the outskirts of the city.
Car chases are a blast. Once you kill the first few waves, they will come at you with increased numbers. Usually 2 or 4 to a vehicle. Use this to make some memorable car chases through Los Santos.
If you hide in the strip club, the security will shoot back at them. It's hilarious to see bullets an strippers zip back and forth. Tities and ass running for their lives...ahhh good times....
Also, if you hide behind the counter in an Ammu-Nation store, the store clerk will shoot them back. (DO NOT SHOOT BACK) The clerk will shoot you! Eventually the clerk gets killed but that leaves you in a nice spot for some shooting action.
Another benefit to this, is that they will drop ammo and money. Eventually it adds up to some decent change...enough to cover the medical bills when you constantly hit the back of a car going 100 mph and fly through the windshield. (Happens to me all the time).
Try it out. It's a ripping good time!