General

• R. Gross, A. Marx: Festkörperphysik (online via heidi)
• N.W. Ashcoft/Mermin: Solid State Physics
• S. Hunklinger, C. Enss: Solid State Physics (onlina via heidi)
• C. Kittel: Introduction to Solid State Physics
• Ibach/Lüth: Solid State Physics (German version online via heidi)
• Quinn, John J.: Solid State Physics : Principles and Modern Application (online via heidi)
• Patterson, Bailey, Solid-state physics (online via heidi)

General - more sophisticated theory textbooks (but really good stuff)

• D.I. Khomskii: Basic Aspects of the Quantum Theory of Solids: Order and Elementary Excitations (Table of contents)
• D.I. Khomskii: Transition metal compounds (online via heidi)
• P. Fazekas: Lecture notes on electron correlation and magnetism
• J. Ziman: Principles of the theory of solids

Electronic properties and bands:

• J. Singleton: Band theory and electronic properties of solids

Semiconductors, optical properties:

• Mark Fox, Optical Properties of Solids, Oxford University Press, 2nd edition

Superconductivity

• Buckel/Kleiner: Supraleitung (the textbook on SC)

Magnetism

• S. Blundell: Magnetism in Condensed Matter (comprehensive overview)
• W. Nolting, A. Ramakanth: Quantum Theory of Magnetism (theory textbook)
• N. Majlis: The Quantum Theory of Magnetism (theory textbook)