There sure are quite a few Pokemon I thought I'd never put into my teams rotation.
Scyther is a for sure. I always wanted one, but they were so hard to catch, until I just caught him one day, first Safari Ball.
Victreebel on my most recent LG team- I've only ever raised one before, and I never thought I'd raise one again, but I decided to.
Dodrio is another, raising one right now in FireRed.
The Geodude line is one I certainly never expected to raise, but they sure can do some damage.
Pelipper, Roselia, Exploud, Altaria, Aggron, Ludicolo, Delcatty, quite a few from Generation III that I ended up raising when I initially had no interest in raising them.
There's so many more Pokemon I thought I wouldn't raise in my 10+ years of playing the games, but so hard to remember all of them, haha. A few I have yet to raise are Muk, Weezing, Jynx and Pinser, but I'll get around to it eventually.