Yes, I strongly miss the days of cheat codes. My siblings and I would use GameGenie (Super Nintendo) and GameShark (Nintendo 64) to have all kinds of fun. When you have significantly less money, replaying games endlessly with various cheats on dramatically extended playability.
As for the most memorable, I will forever have the following codes burned into my memory for codes built into NBA Jam Tournament Edition:
- Left, Right, A, B, B, A: Monster Jam from anywhere on the court
- Down, Right, Right, B, A, Left: Always on Fire
The codes in NBA Jam and Mortal Kombat were interesting, as you had limited time and/or slots to input them, and there were far more than you could input, so each time you played was an opportunity for a unique experience. No small wonder that they were ported to console by the same teams.
One of the reasons I especially like my Dreamcast, and just purchased a DC Digital for it, is that it is the newest console that I own that has a GameShark (a real GameShark, not the later, game save only versions).
People who didn't grow up with cheat codes, either in-game or the cartridge add ons don't understand the importance to those who did. Losing cheat codes in modern games leaves a massive gap in the video game experience, like losing a genre. Can you imagine if one of your favorite genres just ceased to be released on Next-Gen consoles and every generation afterwards?