Oh, boy... Well... I don't remember ever cheating during my first playthrough in any game, unless the mods that add extra hair options and such count. Afterwards, however...
In Baldur's Gate, I roll the dice so long until I get my character stats I am happy with. That can take many, many throws.
I cheated my way through Neverwinter Nights as regards my character's alignment. I wanted to play a druid, but this class only allows you to level up with Neutral alignments. I, being the goddamn goody two shoes that I am, can never keep the neutral alignment for long, though. (The evil points tend to be somewhat scarce, too.) I also think it's silly we can't have nice or mean druids. What's up with that? So I added some points here and there to keep my character Neutral despite otherwise swaying towards good or evil with their actions.
I also exploited NWN's companions. If you keep a companion in your party, they eventually tell you more things about themselves as the story progresses. You get their trust. In the end, they give you an item with great stats as a gift. What I did is that I picked them up in the tavern after the story progressed, talked to them right there and then until they ran out of dialogue, then eventually collected the awesome item. Afterwards I dropped the companion and moved onto another. I always returned to my favourite companion and left the tavern with them, though, wearing all the cool trinkets and leaving all my suddenly gained friends behind. (I did enjoy talking to them, though.) Something tells me the game wasn't meant to be played that way... ahem.
In NWN2, I thought it was unfair that all the companions had extra skill points, so I added a few to my character to "even it out".
Not sure I will ever repeat the NWN and NWN2 ones on new playthroughs, but I have done those things before and have no excuse. 
In DAO, I like adding more armours and weapons. However, I usually try to delevel them with other mods so that their stats are much more reasonable. The fact is, however, that the bonuses (which I haven't figured out how to lower or remove just yet) remain and are quite generous on some of those items. My intention is mostly to get stuff that looks good rather than being OP, though. (I increase the difficulty to even it out sometimes, too.) I even used some armours that barely had any decent stats, just because I thought it fit the character. However, yeah, I do that.
In DAII... Hm. I can't remember much besides the fact that I once tried to add more rivalry points to Isabela so that I could see her return with the Tome for goddamn ONCE. It didn't work, though. Not even on 100% rivalry. Hell, I tried. Honestly and dishonestly. I don't know any more. Screw that criminal scum.
In DAI, I use the Cheat Engine to turn my character's staff into the Sunless Staff... because she doesn't officially go through Champions of the Just (It's part of my headcanon for that character, though.), but that staff is just so pretty and thus I need it for reasons.
In Mass Effect 3, I unlock the Citadel DLC's armour that you get by winning the Armax Arena. I have already played through and won that, but when you start a new playthrough, you have to do it all over again. Given that I like to play the DLC at the end of the game, I'd have to wait for the armour the entire game and then would barely get to use it. So I unlock it at the start of the game instead so I can use it as I see fit.
That's all I can remember at the moment.