Cancel, Refund, Change Tips
Budget Travel Online has a list of 10 Tips to Cancellation, Change, and Refund Policies that seem relatively evergreen. I say relatively, because as quickly as airlines can sell a window seat, that's how quickly a policy can change. That aside, these are ten good guidelines to consider before booking trips.
Also, there are links to major airlines' refund policies so you can see what specific airlines offer for refunds currently.
The biggest thing to keep in mind: there is no universal cancellation policy in the travel industry. Each supplier, each airline, each hotel, travel operator (Expedia, etc.) has their own version. Read the fine print on each and never be shy to ask questions.