Numpad 1: Add Cash - to use this, enter the garage and then press this key. Each keypress adds 1 million dollars. You will have to save and load the game OR buy something to see that it has changed.
Numpad 2: Quick Win - this is a powerful option. Turn this option on and when you pass through the next checkpoint on the racetrack, the race will complete. In most cases this is an instant win. If the race requires some other item to be completed, then you will end the race but may have to do the required part of the race to 'complete' it, such as timed races, etc.
Numpad 3: Add Event XP - do NOT press this key unless you are in an actual race and the XP bar is visible at the top of the screen. Each keypress adds more XP. You can level up very quickly this way, enabling you to buy or aquire more items/cars/upgrades/races, etc.
Numpad 4: Unlock Career Sets - you can use this to open up all the Sets of events before you have the required level. For instance you can open the Drift set of races even though they are locked if you are below level 4.
Numpad 5: Unlock Events - this allows you to enter ANY event, even if the event is locked or requires a badge that you do not have.
Numpad 6: Reset Race Timer - press this key and the current timer for the race will reset to 0 and begin counting up again. Use this to complete certain timed races or to simply reset the timer. May not work in all instances but was tested on races where you have to beat a certain time to complete the course. The best use is to press this just before you complete a lap.
Numpad 7: Unlimited Nitrous - this is for PLAYER ONLY, which is important since improper creation of this option by other trainers causes the AI to have unlimited nitrous (OOPS!). At any rate, toggle this on to allow unlimited use of nitrous in cars equipped with it.
I haven't got my game yet, so I can't wait It is nice to see people coming up with ideas but I still see that Freeze AI isn't put on the Trainer and I love Freeze AI on racing games So here's my ideas: