the saibamen, which are literally just plants that can explode

they're a powerful race of unstable alien plant dudes that freeza's soldiers carry around as backup because they're really strong

Cell Jr which is basically just a stronger saibaman

they're literally as strong as cell himself, they just don't seem to be as refined in technique

that means that until gohan got big mad they were roughly tied for strongest lifeform the universe had ever seen (until later arcs retconned that)