The Age of the Pussyfoot - Fred Pohl
This book was waaaaay ahead of its time. A wonderful short novel from the 1960's that is still a great read. Pohl pretty consistently produces good books. 'Black Star Rising', 'The World at the End of Time', the Gateway series (although hardly obscure) and a whole lot of others.
Riddley Walker - Russell Hoban
A post-apocalyptic novel. Excellent. Would help to have some local knowledge of English culture.
Dying Inside - Robert Silverberg
This book does not get enough recognition.
The Lilith's Brood series - Octavia Butler
Three novels about the integration of the human race by aliens after a nuclear war. Marvelous.