Hinei Ma Tov is a niggun connected with Lag B’Omer. This is both because one of the most famous teachings of the Rashbi is on this Possuk, and because its subject is Ahavas Yisroel, a major theme of Lag BaOmer.
Reb Shmuel Zalmanov writes in Sefer Haniggunim, that this Niggun originates from Sfardishe Yidden living in Eretz Yisroel. He heard it from his father Reb Shraga Feivesh Zalmanov. The way it is transcribed Sefer Haniggunim, however, is different from the original tune.
Another slightly different version is that of Pinya Althoiz, with more of a Chabad overtone. This version also contains two more stanzas, presumably added later, which repeat over and over.
The popular version is found on Nichoach without any trace of its Sefardic origins, with the last two stanzas also played with music. Interestingly, by the Rebbe it was sung without the two last parts.
There are two other Chabad Niggunim to the words ”Hinei Mah Tov”: one begins with the same tune as “Sisu V’simchu” and was sung several times by the Rebbe’s farbrengens, the other is Niggun No. 254 in Sefer Haniggunim.
Reb Shmuel Zalmanov (original version)
By the Rebbe (popular version)