Category Hierarchy and Resolving Product Membership

[cancan101]

What is the best way to model Categories (that are in a Hierarchy) and Products (which belong to one or more leaf Categories). Ideally I can easily answer the question: What Products are in this Category or any child category.

For example:
Categories:

• Vehicles (non-leaf)
  • Cars (leaf)
  • Trucks (leaf)
• Toys (non-leaf)
  • Legos (leaf)

Products:

• A (Cars)
• B (Cars; Legos)
• C (Trucks)
• D (Legos)

and I want to answer the question "What Products are 'Vehicles'?"