Biomechanics: "Normal and Abnormal Function of the Foot and Ankle", Root et al; "Clinical Biomechanics of the Lower Extremity", Valmassy
Podiatric Medicine(including all pathologies): Too many to really chose from. I still refer to Harrison's Internal Medicine text. Its full body, systemic medicine, but applies to all of our practices. "Physical Examination and History Taking", Bates; "Essentials of Internal Medicine in Clinical Podiatry", Zier (this one is really meh imho)
Podiatric Surgery: McGlamry's Text, "Textbook of Bunion Surgery", Gerbert; "Pediatric Foot and Ankle Surgery", Jay; "Clinical Pediatric Orthopeadics", Tachydjian. Myerson has an excellent foot and ankle Surgery text as well.
Radiology: "Bone and Joint Imaging", Resnick
MRI: William H. Simon D.P.M. has an excellent MRI text. The name is alluding me atm. He is a local colleague of mine. Brilliant man.
Dermatology: "Color Atlas and Synopsis of Clinical Dermatology", Fitzpatrick; "Color Atlas of Cutaneous Disorders of the Lower Extremities" Witkowski and Lemont. Harvey was a professor of mine as is a pathology genius. The only Podiatrist to ever pass the Pathology examination given to the M.D. Pathologists.
Textbooks are for reference. Please realize that this is not an exhaustive list, but what I still use today even after ten years in practice. In practice its wise to keep with the latest journals as things change quickly, but these texts really give an excellence basis to build on.