Migration of Men - About 300 or so years after the Noldor established their homes in Beleriand, Men arrived.  The first Elf to gaze upon the race of Men (that we know of) was Finrod, son of Finarfin.
 

"Finrod Felagund lord of Nargothrond journeyed east of Sirion and went hunting with Maglor and Maedhros, sons of Fëanor.  But he wearied of the chase and passed on alone towards the mountains of Ered Lindon that he saw shining afar; and taking the Dwarf-road he crossed Gelion at the ford of Sarn Athrad, and turning south over the upper streams of Ascar, he came into the north of Ossiriand.  In the valley among the foothills of the mountains, below the springs of Thalos, he saw lights in the evening, and far off he heard the sound of song.  At this he wondered much because the Green-elves of that land lit no fires, nor did they sing by night.  At first he feared that a raid of Orcs had passed the leaguer of the North, but as he drew near he perceived that it was not so; for the singers used a tongue that he had not heard before, neither that of Dwarves nor of Orcs.  Then Felagund, standing silent in the night-shadow of the trees, looked down into the camp, and there he heheld a strange people." ~The Silmarillion, chap. 17 (Of the Coming of Men into the West)