Essentials:
Hoppenfeld's Surgical Exposures in Orthopaedics
Campbell's Operative Orthopaedics
Rockwood & Greens Fractures in Adults & Children (alternatively Musculoskeletal Tauma)
Master's Techniques in Fractures
Miller's Orthopaedic Review

Less essential but great books:
Lovell & Winters Pediatric Orthopaedics
Green's Operative Hand Surgery
Most of the books in the Master's Techniques series