Há também Beren, que morreu no final da Caça do Lobo. Carcharoth, o maior lobo que jamais viveria, já havia mordido a mão de Beren e enlouquecido pela dor da Silmaril queimando sua barriga. Ele foi perseguido por Beren, Huan, o cão e os elfos de Doriath, e apesar de Carcharoth ter sido morto, Huan e Beren foram mortalmente feridos.

Gandalf

Como um Istar e, portanto, um Maia, sua verdadeira natureza é de um espírito santo, e sua forma física é apenas um encarnação , um avatar .

Afirma-se que o próprio Eru interveio (presumivelmente de uma forma excepcional, já que esta não parece ser a norma) e concedeu ao seu espírito "voltar" ao seu corpo mais uma vez, porque ele era o único Istar que permaneceu fiel à sua missão original.

Esta nova reencarnação não era exatamente a mesma de antes: ele era conhecido anteriormente como Gandalf, o Cinzento , mas quando ele foi trazido de volta à vida ele fez na forma de Gandalf, o Branco : o seu verdadeiro potencial foi agora revelado.

The wizards, also called Istari, were originally spirits of the order of the Maiar, the followers of the Valar. These were sent by the Valar to help and assist the peoples of Middle-earth against Sauron as he gathered his forces during the Third Age.
[...]
Their spirits remained immortal, and they aged only very slowly. However, their bodies could be killed: Gandalf did indeed die from his duel with the Balrog of Moria, and only through the intervention of Eru himself was he restored to his body.
_{Tolkien Gateway, Wizards}

Gandalf used his last measure of strength to slay the Balrog, throwing him down the mountainside in ruin. Gandalf's spirit then left his body, having sacrificed himself to save the Fellowship.
[...]
But Gandalf's spirit did not depart Middle-earth forever at this time. As the only one of the five Istari to stay true to his errand, Olórin/Gandalf was sent back to mortal lands by Eru, and he became Gandalf once again. Yet, as he was now the sole emissary of the Valar to Middle-earth, he was granted the power to "reveal" more of his inner Maiar strength. This naked power that lay within him was seldom used during the remainder of his time in Middle-earth, as his mission was essentially the same: to support and succour those who opposed Sauron. Nevertheless, when Gandalf's wrath was kindled his "unveiled" strength was such that few of Sauron's servants could withstand him.
_{Tolkien Gateway, Gandalf}

Glorfindel

Normalmente, quando um Elfo morre, seu espírito vai para os Salões de Mandos onde ele espera ser reencarnado e ficar em casa. Aman.

Glorfindel teve a chance única de voltar à Terra-média depois de sua reencarnação.

Glorfindel’s spirit passed to the Halls of Mandos, where he waited with the spirits of the other Noldor who had died during their war against Morgoth. But because of Glorfindel’s noble actions in life, his reluctance at the Exile, and his furthering of the purposes of the Valar by saving Tuor and Idril, he was re-embodied after only a short time. He had redeemed himself, and was purged of any guilt. Not only did his sacrifice get him an early pardon, it earned him great powers, so that he was almost an equal to the Maiar.
Eventually, Manwë sent him across the sea to Middle-earth, possibly as early as Second Age 1200, but more likely in 1600 with the Blue Wizards. If the latter date, he arrived just after the One Ring had been forged, Barad-dûr built, and Celebrimbor dead or soon to be so. While the Blue Wizards were sent to the east, Glorfindel’s mission was to aid Gil-galad and Elrond in the struggle against Sauron. He played a prominent behind-the-scenes role in the war in Eriador and the other struggles of the Second Age and Third Age. His part, though great, was mostly overlooked by the histories, because his immense, angelic power was not usually displayed openly.
_{Tolkien Gateway, Glorfindel}

Durin

Durin I, chamado o Imortal foi o primeiro e principal dos Sete Pais dos Dwarwes. Os anões acreditavam que ele iria reencarnar para viver sete vidas, todas as vezes com o nome de Durin.

Todos os reis nomeados Durin que seguiam Durin I (de II a VII) se pareciam muito com os Imortais tanto na aparência quanto nas maneiras, dando crédito a essa crença.

The Longbeards believed that Durin would return to them seven times, and in each reincarnation he will again be named Durin and reign as King. He did have six descendants that were named Durin, all were kings of Durin's folk.
_{Tolkien Gateway, Durin}

Sim, muito poucos.

Homens

Beren foi o único.

None have ever come back from the mansions of the dead, save only Beren son of Barahir, whose hand had touched a Silmaril; but he never spoke afterward to mortal Men.

(The Silmarillion, Of Men)

Elfos em geral

'Reencarnação' ou re-encarnação é o destino habitual dos Elfos que morrem, ou pelo menos os Eldar. Tolkien expandiu isso em grande detalhe em "Leis e Costumes dos Eldar" e "Athrabeth Finrod ah Andreth", publicado no Anel de Morgoth (volume 10 de A História da Terra Média).

Os detalhes de como isso funciona não são totalmente consistentes, mas parece que Tolkien acabou rejeitando a idéia original de Elfos renascerem como novos filhos

A houseless fea that chose or was permitted to return to life re-entered the incarnate world through child-birth.

(Laws and Customs of the Eldar)

substituindo-o por um 're-housing' em um corpo reconstruído idêntico ao que eles tinham no momento da morte.

[Eru falando com Manwe]

Look and ye will find that each spirit of My Children retaineth in itself the full imprint and memory of its former house

[...]

After this imprint ye may make for it again such a house in all particulars as it had ere evil befell it. Thus ye may send it back to the lands of the Living.'

(Athrabeth Finrod ah Andreth, The Converse of Manwe and Eru)

Em qualquer caso, parece ser o destino normal dos Eldar que morrem, pelo menos se eles quiserem retornar à vida:

The Eldar say that more than one re-birth is seldom recorded. But the reasons for this they do not fully know. Maybe, it is so ordered by the will of Eru; while the Re-born (they say) are stronger, having greater mastery of their bodies and being more patient of griefs. But many, doubtless, who have twice died do not wish to return.

[...]

Concerning the fate of other elves, especially of the Dark-elves who refused the summons to Aman, the Eldar know little.

(Laws and Customs of the Eldar)

Glorfindel

They 'normally remained in Aman'. Simply because they were, when rehoused, again in actual physical bodies, and return to Middle-earth was therefore very difficult and perilous.

(Athrabeth Finrod ah Andreth, Note 3)

Miriel

In Aman only was there no decay. Thus Miriel was there rehoused in her own body, as is hereafter told. (Laws and Customs of the Eldar)

Ainur

Geralmente Ainur não podia "morrer" de forma alguma, já que seus corpos eram apenas roupas temporárias, não essenciais para sua função:

Moreover their shape comes of their knowledge of the visible World, rather than of the World itself; and they need it not, save only as we use raiment, and yet we may be naked and suffer no loss of our being.

(The Silmarillion, Ainulindale)

Gandalf

Este é um caso especial, pois ele era um dos Istari (Magos) - Maiar que foram colocados em corpos "permanentes" e se tornaram seres encarnados como Elfos e Homens. Assim, Gandalf poderia realmente morrer, já que ele tinha um corpo "permanente" real:

Gandalf really 'died', and was changed

[...]

I wd. venture to say that he was an incarnate 'angel'

[...]

By 'incarnate' I mean they were embodied in physical bodies capable of pain, and weariness, and of afflicting the spirit with physical fear, and of being 'killed'

(The Letters of J.R.R. Tolkien. Letter 156.)

Sauron

O último caso é um pouco intermediário entre o usual Ainur e o Istari. Sauron não estava encarnado como os Istari, mas ele tinha se tornado em grande parte ligado à sua forma física fazendo o mal nele, então quando ele foi morto na Queda de Numenor e novamente na Batalha de Dagorlad, ele teve que reconstruir seu corpo. para se tornar "eficaz" novamente.

Estou surpreso que ninguém tenha mencionado O Exército dos Mortos

"The Dead are following," said Legolas. "I see shapes of Men and of horses, and pale banners like shreds of cloud, and spears like winter-thickets on a misty night. The Dead are following."

"Yes, the Dead ride behind. They have been summoned," said Elladan.

Fonte: A Passagem da Companhia Cinza, O Retorno do Rei

Se você contar Dagor Dagorath como canon então Túrin Turambar

In that day Tulkas shall strive with Morgoth, and on his right hand shall be Fionwë, and on his left Túrin Turambar, son of Húrin, coming from the Halls of Mandos; and the black sword of Túrin shall deal unto Morgoth his death and final end; and so shall the children of Húrin and all Men be avenged.

Fëanor também

Then Fëanor shall take the Three Jewels and bear them to Yavanna Palúrien; and she will break them and with their fire rekindle the Two Trees, and a great light shall come forth.

Fonte para ambos, História da Terra Média (Book of Lost Roads)