The Encyclopedia of Things That Never Were by Michael Page
A robust illustrated volume of characters from modern literature, myths and folklore.
Excellent sections on horse-creatures.
Acorna: The Unicorn Girl by Anne McCaffrey and Margaret Ball
Three space miners discover a strange humanoid girl in a rescue pod.
Her ability to purify air and water as well as heal injuries soon
put her life in danger.
The Last Unicorn by Peter S. Beagle
One of the most beloved books about unicorns and self-identity. A unicorn leaves her
forest to find out where her kind have disappeared to, undertaking a dangerous journey.
The Black Unicorn by Terry Brooks
I remember staying up all night to finish reading this one. One of the
books about Ben Holiday, who buys a magic kingdom through a mail order
catalog.
The Birth of the Firebringer by Meredith Ann Pierce
Book One of The Firebringer Trilogy. Long out of print, unicorn fans can rejoice in the reprint of the series about Jan, the Prince of Unicorns.
Dark Moon by Meredith Ann Pierce
Book Two of The Firebringer Trilogy. An unexpected attack by gryphons puts Jan and the herd of unicorns in danger. Swept away by the ocean, he finds himself in a strange place and strangely worshipped.
The Son of Summer Stars by Meredith Ann Pierce
Book Three of The Firebringer Trilogy. With the help of his twin foals, Jan seeks to regain the unicorn's ancestral homeland from the wyverns.