Our friends at AMEE also have a cool API, with a focus on Carbon data (and other GHGs). Since our focus is on Energy Pricing Data, the combined possibilities are really quite exciting. (We hope that developers at the CleanWeb Hack next weekend in San Francisco will mash-up some cool hacks with our combined APIs)
Two potential hacks come immediately to mind: By combining a load profile with Electricity Pricing, developers could provide an accurate, real-time price-of-energy. Add in emissions data from the AMEE apis, and you can deliver some really cool metrics (cost-per-unit, carbon-per-unit) for any given company, in any given region of the US. See for example the MyCoffee hypothetical.
Or, another fun hack could replicate realtimecarbon.org for a given US sub-region (ie. Californa). An ingenuitive hacker could easily build a ‘carbon intensity’ calculator for any electricity subregion in the US. Basically all you need is this link, this link and this link.