The Blue Lagoon is a geothermal spa and the most famous sight in Iceland.

The Gullfoss waterfall is quite spectacular.

the namesake of all geysers, and its neighbour Strokkur which erupts every five minutes or so.
Þingvellir National Park
a beautiful landscape of water-cut lava fields, which is historically important as the site of Iceland's parliament from 930 AD.
Vatnajökull glacier
is in Southeast Iceland and is Europe's largest glacier.

Jökulsárlón, the largest glacier lake in Iceland, is located off Route 1 and part of Vatnajökull glacier.

In the colder months, one may frequently get stunning views of the Aurora Borealis, a.k.a. Northern Lights (http://www.northernlights...) anywhere away from city lights.