Official tourism sites for the country:
Visit Iceland (www.visiticeland.com)
Inspired by Iceland (www.inspiredbyiceland.com)
Each region also has its own useful site/s:
Southwest Iceland (www.visitreykjanes.is; www.south.is)
West Iceland (www.west.is)
The Westfjords (www.westfjords.is)
North Iceland (www.northiceland.is; www.visitakureyri.is)
East Iceland (www.east.is)
Southeast Iceland (www.south.is; www.visitvatnajokull.is)
Useful and practical smartphone apps include the vital 112 Iceland app for safe travel, Vedur (weather), and apps for bus companies such as Strætó and Reykjavík Excursions. Offline maps come in handy.
There are plenty more apps that cover all sorts of interests, from history and language to aurora-spotting, or walking tours of the capital. Reykjavík Grapevine's apps (Appy Hour, Appetite and Appening Today) deserve special mention for getting you to the good stuff in the capital.