Lonely Planet Central Asia by Stephen Lioy et al. -- The standard backpacker guidebook for the region, with a solid Kyrgyzstan chapter covering practical information, trekking routes and accommodation. Updated regularly.
Kyrgyzstan by Laurence Mitchell (Bradt Travel Guides) -- The only dedicated English-language guidebook to the country. Thorough coverage of trekking routes, cultural context and off-the-beaten-path destinations. Essential if you are spending more than a week.
The Day Lasts More Than a Hundred Years by Chingiz Aitmatov -- Aitmatov is Kyrgyzstan's most famous writer, and this novel blends Kyrgyz legend with Soviet-era realism. It captures the tension between tradition and modernity that still defines the country. His other novels, including Jamilia (which Louis Aragon called "the most beautiful love story in the world"), are also worth seeking out.
Manas -- The Kyrgyz national epic, one of the longest poems in the world at roughly half a million lines. It tells the story of the hero Manas and his descendants, and is still performed by manaschi (oral storytellers) at festivals. Full English translations are hard to find, but abridged versions exist. Understanding Manas is key to understanding Kyrgyz identity.
The Great Game by Peter Hopkirk -- Not specifically about Kyrgyzstan, but essential background reading for anyone traveling in Central Asia. The 19th-century rivalry between Britain and Russia for control of the region shaped borders and politics that persist today.
Apples Are from Kazakhstan by Christopher Robbins -- A witty, readable account of Central Asia that covers Kyrgyzstan's post-Soviet transformation alongside its neighbors. Good for understanding the region's recent history without wading through academic texts.