A simple JSON api for fuel prices:
http://www.fueleconomy.gov/ws/rest/fuelprices

and a timeline of global crude oil prices:
JSON: https://www.quandl.com/api/v3/datasets/OPEC/ORB.json
XML: https://www.quandl.com/api/v3/datasets/OPEC/ORB.xml
- The graph it produces.. https://www.quandl.com/data/OPEC/ORB-OPEC-Crude-Oil-Price