It looks like Edmonton outsourced this to Microsoft for their OGDI Azure offering and it should provide a set of APIs: http://ogdisdk.cloudapp.net/
Seattle is apparently going with Socrata which offers APIs
San Francisco and others are also trying to create some open source solutions in this space, see: http://ideas.topplabs.org/wiki/Data#Data_Catalog_Systems
I know RDF has a lot of support in the UK and RDF is an interesting case because it is basically just flat files, but the files themselves can act like a web API (with say a SPARQL query)
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