Oh yes. This topic I answer with so many pokemon. Let's start.
Oddish and Bellsprout family.
These six Pokemon, with the introduction of Jumpluff, a much much cuter version of them, had been extremely forgotten. I don;t know what people found in Jumpluff, but these six are more badass than him. Two cool and very original concepts. Two forgettable pokemon. Sad for them.
Mankey Family.
We all know the story behind Ash's Primeape, and his short-lived TV appearance. Have we seen him again after that? No right? Even ingame players rarely used this pokemon, and even rarer on competitive play. IMO, Primeape has one of the most beautiful design ever made.
Doduo family.
I myself have forgotten about the existence of these two flightless birds. They have nothing special about them, except that they can learn Fly, although they are based on flightless birds.
Seel family.
Being found only on a few, selected routes on Kanto (ain;t even sure if it is found anywhere else in the world), having probably subpar stats, limited movepool, a weak typing; all of this contributed to this family's extinction from the pokemon world.
Krabby Family.
Another pokemon of Ash's that had very few anime appearances, despite having proven to be a powerhouse. Ingame-wise, Kingler has not anything to boast of that other Water-types cannot, except a previously exclusive move, Crabhammer.
Tangela.
Yes, you may argue that Tangrowth is a good Pokemon. But how many of us actually remembers Tangela when we are not in need of Tangrowth (who is not a famous pokemon either?)
Goldeen Family.
Gender bender. A queen evolves to a king. Seems legit. ANYWAY, like Kingler, Seaking cannot actually stand out amongst any choices as it has nothing special to offer, except, I don't know. A GenI waterfall move I guess?
Lapras.
I cannot believe how people keep on forgetting many of Ash's Pokemon. despite her brief appearance during the Orange Island arc, Lapras is quite capable of many things. The ability to learn Horn Drill, Sheer Cold, and Fissure is epic and novel. it's design is great. People forget Lapras once dominated the OU tier.