The most popular is to the ruins of Choquequirao and back (in & out of Cachora) in 4 days, 4 nights.
What guidebooks do you recommend?
Lonely PlanetTrekking in the Central Andes. LP is our favourite hiking guide, by far. Unfortunately it does not include this trek.
As of this writing there are no trekking guides we can recommend for hiking past the ruins. The best you can do is to purchase a small booklet from South American Explorers called the ALTERNATIVE INCA TRAILS INFORMATION PACKET.
There are hundreds of books on Machu Picchu. Browse the book shops when you get to Cuzco for a souvenir book which also serves as a guidebook for touring the ruins.