From Wikipedia's article on the subject...
http://en.wikipedia.org/wiki/Norse_colonization_of_the_Americas
Settlements in continental North America aimed to exploit natural resources such as furs and in particular lumber, which was in short supply in Greenland.[12] It is unclear why the short-term settlements did not become permanent, though it was in part because of hostile relations with the indigenous peoples, referred to as Skrælings by the Norse.[13] Nevertheless, it appears that sporadic voyages to Markland for forages, timber, and trade with the locals could have lasted as long as 400 years.
Evidence of continuing trips includes the Maine Penny, a Norwegian coin from King Olaf Kyrre's reign (10671093) allegedly found in a Native American archaeological site in the U.S. state of Maine, suggesting an exchange between the Norse and the Native Americans late in or after the 11th century; and an entry in the Icelandic Annals from 1347 which refers to a small Greenlandic vessel with a crew of eighteen that arrived in Iceland while attempting to return to Greenland from Markland with a load of timber.
The question was definitively settled in the 1960s when a Norse settlement was excavated at L'Anse aux Meadows in Newfoundland by archaeologist Anne Stine Ingstad and her husband, outdoorsman and author Helge Ingstad. The location of the various lands described in the sagas is still unclear however. Many historians identify Helluland with Baffin Island and Markland with Labrador. The location of Vinland is a thornier question. Most believe that the L'Anse aux Meadows settlement is the Vinland settlement described in the sagas; others argue that the sagas depict Vinland as being warmer than Newfoundland and that it therefore lay farther south.
In 2012, possible signs of Norse outposts in Nanook at Tanfield Valley on Baffin Island, as well as Nunguvik, Willows Island and the Avayalik Islands, were identified by Canadian researchers.[17][18][19] Unusual fabric cordage found on Baffin Island in the 1980s and stored at the Canadian Museum of Civilization was identified in 1999 as possibly of Norse manufacture; that discovery lead to more in-depth exploration of the Tanfield Valley site.