The classic textbook for analog transistor-level design is Analysis and Design of Analog ICs by Gray and Meyer (mentioned in a footnote). It assumes a strong background and goes more for comprehension than building insight so I wouldn't recommend it initially. For actual design, Behzad Razavi's books are great to gain insight. I really enjoy his pedagogical approach. Agarwal and Lang have a good sophomore/junior level book as do Sedra and Smith (Razavi's microelectronics book is also good).
Art of Electronics always deserves a mention in circuits book discussions. The former books all take more rigorous approaches to things while AoE focuses strongly on practical insight. It's less of a textbook than the others (fewer equations) but includes many real examples of circuits, from simple to very complex.