I nightweaned at around 6 months, and did CIO at 8 months, because my son was relying on me as his "habit" in order to be able to sleep, and nothing else we tried worked.
That being said, we've had several regressions (usually after a weekend trip away from home, or after an illness--if he's sick, I get him).
He's currently 27m, and he wakes up (maybe from dreams, I think?), and if he's not sick, I go in and hug him and tell I love him, that he's safe, and that it's time for sleeping and that Momma is going to go back to sleep. Then, I go back to bed..... Most nights, despite his protests when I'm in the room, he does go back to sleep with little to no vocal resistance. Occasionally, though, it turns into "Momma I'm scared; Momma I have a poopy diaper (no he doesn't! LOL); Momma I cant find my Charlie Mouse; etc.).... For these, I might get up 1 more time and repeat that it's sleepy time/time to sleep & Momma is going back to sleep.... Then, I don't go back into his room until it's time to get up (or a reasonable facsimile---if he is still fussing at 6 or 6:15, and he normally gets up at 6:45, I'll go get him and we'll start the day).
It's not a perfect solution, but it's better than him sleeping with us (he is not a fun co-sleeper!), or me rocking him in the rocking chair, or standing next to his crib for an hour till he falls asleep.....
I do dread the transition to a toddler bed, because I'm afraid we're going to have lots of transition problems with that......... :)