Update: Download link fixed, sorry about that.
Just after I post about the +10, +13 trainers it looks like we have something alltogether way better. PiZZADOX has released the trainer of all trainers (at least for the time being!).
Unzip/Unrar trainer into your game directory, then start trainer with “pztrain.exe”. Start the game using the launch button. During gameplay toggle trainer options by pressing the following key combinations:
Hotkey Option F6 Toggle Infinite Health F7 Toggle Infinite Armor F8 Toggle Infinite Ammo F9 Toggle Infinite Run F10 Toggle Infinite Breath Shift+F6 Toggle Infinite Nitrous F11 Increase Money 3 No Wanted Level 5 Max Wanted Level 6 Toggle One Hit Kill 7 Toggle Bulletproof Vehicles 8 Toggle One Hit Exploding Vehicles 9 Toggle Freeze Mission Timer 0 Toggle Freeze Game Clock Shift+3 Get Maximum Muscle Shift+5 Get Maximum Stamina Shift+6 Toggle Max/Min Fat Shift+7 Get Maximum Respect Shift+8 Get Maximum Gambling Skill Shift+9 Get Hitman Level on All Weapons Shift+0 Get 100% Completion Shift+F7 Get Maximum Lung Capacity Shift+F8 Get Maximum Bike/Driving/Cycling/Flying Skill Shift+F9 Get 100 Tags Shift+F10 Get 50 Oysters Shift+F11 Get 50 Snapshots Shift+Del Get 50 Horseshoes F12 Toggle In-Game Menu*
Additional notes about the functionality of these are available in the info file attached to the trainer. Download the trainer now from GTA Garage.