Senzu beans are commonly used throughout DBZ. They are grown by Korin half way between earth and Kami's Palace. It fully restores you energy and heals you to perfect health. If a Saiya-Jin is brought almost to death and they are healed to full power they become very strong.

Cell-
1.Goku gave him one when he wanted the match between Gohan and Cell to be fair.

Goku-
1.He eats one leaving Kamis Tower going to earth
2.Eats 4 training on a ship towards Namek
3.Eats on ship
4.Eats on ship
5.Eats on ship

Gohan-
1.Gets half of one after being beat by Nappa
2.After getting Crushed by Recoome

Krillin-
1.Gets half after being beat by Vegeta
2.Gets on after Recooms boomkick
3.gets on after being hit by cell
4.Gets on from being beat by Cell jr.'s

Piccolo-
1.Gets one after being beat by Nappa
2.After energy being drained by android #20
3.He gets one after fighting Android #17 & #18
4.After being beat by Cell jr.'s
5.Gets one during Majin Buu fight

Tien-
1.After being beat by Android #17 & #18
2.After doing that Triangle attack on Cell
3.Gets on after being beat by Cell Jr.'s

Vegeta-
1.After being beat by Cell jr.'s
2.After almost being killed by Cell

Videl-
1.Gets on after fighting in the Budoukai

Yamcha-
1.gets on after getting a hole in his stomach by Android #20
2.After being beat by Cell jr.'s

I will add more as I see them eaten in the series.