Socialist figures, socialist organizations, wars in which socialist factions played a heavy role. Anything on the topic would be great. I even live somewhat near the University of Florida, which is supposed to have a superb Latin American, and especially Caribbean, selection. So feel free to challenge them with obscure quality volumes.
For the record, I did check out the book list, which was quite good, but light on the subject of socialism in Latin America specifically.
A few books I used for a paper on Raul Castro that I didn't notice on the book list:
Cuba: Castroism and communism,: 1959-1966 by Andres Suarez. This book was published in 1967 so it will most likely feel like a current events book rather than an actual history book.
The Cuban Revolution: Origins, Course, and Legacy by Marifeli Perez-Stable. A new edition of this book just came out in 2011 and covers Cuba's revolution from the start of the 20th century.
Bay of Pigs: The Untold Story by Peter Wyden. This is more a military history than history of socialism, so it might not be what you're looking for. But, it involves Cuba, so I'll list it for you.