Great Ireland
AKA Irland it mikla; Hvítramannaland; Hibernia Major

A presumably-phantom island in the Atlantic, thought to be near Vinland (eastern Canada). It is identified with the Chesapeake by Reeves, et al., while Ellwood identifies it with South America. While the second is unlikely, the identification with the Chesapeake, at least in terms of identifying a particular landmass visited by Vikings, may not be entirely wrong, as it pretains to an area along the Eastern Seaboard.

At any rate, the actual identification of Great Ireland is impossible, as so little information is given, except that it is a land near Vinland. That "Eyrbyggja Saga" mentions the people speaking Irish is not necessarily proof of a pre-Colombian Irish settlement in North America. There are a number of possible explanations: first, Iceland was settled first by the Irish, whome were still living there when the Norse arrived. There were other Goidelic-speaking lands conquered by the Norse, also, specifically the Isle of Man and Scotland. Third, the story of an Irish settlement beyond Iceland may be not a memory of the previous settlers of Iceland, but also an influence from the medieval legend of Saint Brendan, who is supposed to have sailed the Atlantic as far as the Sargasso Sea.

References
The first mention of Great Ireland is in the Landnámabók, which dates from around 1300:

Ari, who was drifted over the ocean to Whitemans'-land, which some call Ireland the Great, and lies west away in the ocean anigh to Vineland the Good; thither men hold that there is six days' sailing from Ireland due west. Ari could not get back from this country and there he was christened. This tale was first told by Hrafn the Limerick trader who had spent a long time in Limerick in Ireland. Thorkel, the son of Gellir said that Icelanders, who had heard Earl Thorfin of Orkney tell the tale, avowed that Ari had been recognised in Whitemans'-land

In the "Saga of Erik the Red", the people of Markland--Laborador--describe Great Ireland as such:

They stated, that there were no houses there, and that the people lived in caves or holes. They said that there was a land on the other side over against their country, which was inhabited by people who wore white garments, and yelled loudly, and carried poles before them, to which rags were attached; and people believe that this must have been Hvitramannaland [White-men's-land], or Ireland the Great.

There is a third mention of the island in "Eyrbyggja Saga", though the land is unnamed:

But so it befell at last that they were ware of land; a great land it was, but they knew nought what land. Then such rede took Gudleif and his crew, that they should sail unto land, for they thought it ill to have to do any more with the main sea; and so then they got them good haven.

And when they had been there a little while, men came to meet them whereof none knew aught, though they deemed somewhat that they spake in the Erse tongue.

SOURCES
Anonymous. "Eyrbyggja Saga" The Saga Library, Vol. Ii: The Story Of The Ere-Dwellers, translated by William Morris & Eirikr Magnusson (Bernard Quaritch, London, 1892. URL: http://omacl.org/EreDwellers/. Anonymous. "The Saga of Erik the Red". The Norse Discovery of America. ed. by Arthur Middleton Reeves, North Ludlow Beamish, and Rasmus B. Anderson. New York: Norrśna Society, 1906. URL: http://www.sacred-texts.com/neu/nda/nda00.htm.

Ari The Learned. Landnámabók. The Book Of The Settlement Of Iceland. Ed. And Trans. Rev. T Ellwood, M. A. London: T. Wilson, 1898. URL: http://www.northvegr.org/lore/landnamabok/titles.php 1898