The War of the Last Alliance
Seeing as the Last Alliance is so important and all, here's a little bit about it and some pretty pictures (Renee thinks they're pretty anyway).  Ok so, back in the second age, Sauron taught the elvish smiths how to make nifty rings, etc., they made they three elven rings, Sauron made the one and betrayed them.  He covered the land in darkness and such.  Which is where the Last Alliance comes in.  Gil-galad, the High King of the Noldor, and Elendil, the leader of the Númenorian refugees, decided that their only chance was to band together and face Sauron instead of dividing their strength and being conquered individually.  With this in mind, they formed an alliance--the Last Alliance of Elves and Men. 
Gil-galad
(click for more on Gil-galad)
They marched east towards Mordor, stopping in Imladris.  According to the account in the Silmarillion it was the fairest host that has since been seen and the largest since the Great Battle at the end of the First Age.  From Imladris they marched on to Dagorlad ("battle plain").  There they faced the hosts of Sauron, Elendil with his sword Narsil and Gil-galad with his spear Aeglos.  They won and marched on
into Mordor itself and attacked Barad-dur.  They laid siege to it for seven years, many elves and men died--including Elendil's son Anarion.  Eventually, they attacked it and Sauron himself came out to fight.  Both Elendil and Gil-galad fought Sauron and were killed, and the sword Narsil was broken.  Sauron was also destroyed (for the time being), and Isildur cut the One Ring
Part of the Elf Host
Isildur with Narsil
from Sauron's finger using the hilt-shard of Narsil.  Isildur took the ring for himself, as restitution for his slain father and brother.  He would not throw it into Orodruin despite the advice of Elrond and Cirdan-they alone knew what Isildur had taken as only they and Isildur had faced Sauron with Gil-galad and Elendil.  Isildur then rode to Minas Anor (later Minas Tirith) and planted the White Tree in memory of his brother.  He was later slain at the Gladden Fields and the ring was consequently lost.
Gil-galad died.  Narsil broke under Elendil as Sauron wielded the ring.  Isildur used the Hilt-shard of Narsil to cut the ring from Sauron thereby destroying him (at least for a while of course).  Isildur then took the ring.  Elrond then lead Isildur into the cracks of Doom and tried to convince him to throw the ring into Orodruin and destroy it.  Isildur did not, and he was later killed at the Gladden Fields and the ring was lost.
And now for the movie version (or just some differences with the book account):  Elves and Men formed the last alliance under Gil-galad and Elendil.  They fought Sauron upon Dagorlad then marched into Mordor.  They fought Sauron on the slopes of Mt. Doom, and Elendil and
Regarding Thranduil and Oropher:
Oropher fell in this war, and the host from Mirkwood suffered heavy casualties.  Thranduil survived and went back to Mirkwood as King (at least one version goes that way).
Elrond near Mt. Doom
(click for more on Elrond)
LOTR Things
Legolas