I found this taxonomy of code smells by Mika Mäntylä very interesting. The smells are mostly straight out of Refactoring but the groupings are new:

• The Bloaters, things that have grown so large that they cannot be effectively handled
  • Long Method
  • Large Class
  • Primitive Obsession
  • Long Parameter List
  • DataClumps
• The Object-Orientation Abuser, cases where the solution does not fully exploit the possibilities of object-oriented design.
  • Switch Statements
  • Temporary Field
  • Refused Bequest
  • Alternative Classes with Different Interfaces
• The Change Preventers, things that hinder changing or further developing the software
  • Divergent Change
  • Shotgun Surgery
  • Parallel Inheritance Hierarchies
• The Dispensables, things that should be removed from source code
  • Lazy class
  • Data class
  • Duplicate Code
  • Dead Code
  • Speculative Generality
• The Couplers, cases that increase coupling
  • Feature Envy
  • Inappropriate Intimacy
  • Message Chains
  • Middle Man