I used action replay on Nintendogs, all I could get for my version was like max trainer points and max money or something, and I only used it because I had already gone through the entire game and gotten all the trainer points on my own and just decided one day for some idiotic reason that I wanted to reset. When I realized everything I had actually lost by resetting I got pretty mad at myself, so I borrowed a friends AR and used it to at least unlock the dogs you get via trainer points. Other than that.... No. I cheat on The Sims though, I figure it's an unbeatable game that I just play for fun, I want to enjoy it not spend the whole time trying to get my sim a job so I can buy the furniture I want to have or build the house I want. I used to use all sorts of walkthroughs too, but now that isn't fulfilling enough so I just run around like an idiot for 2 hours in the fire temple in Master Quest OoT until I figure out that all I had to do was stand on a switch and run through the door it opened.... YEAHHHHHH. Hahahaha.
When I was younger I remember playing the first three Spyro games, but I couldn't figure out the boss fights and I was afraid of the bosses so my "cheat code" was my dad played all the bosses for me. XD