I've found a list of government forms at the US federal level by looking at the OIRA PRA Information Collections XML file. Is there a list of similar forms at the state/local level for the US?
There is definitely no such list for Washington, DC (Government of the District of Columbia).
There was forms automation project back in 2006/2007 where some forms where converted to database backend using LiquidOffice tool. You can see list of all currently published forms for DC.gov here http://forms.dc.gov/index.html (click Forms on the left). But beware, there are plenty of forms that are just stan alone PDFs or custom webpages.
While surely not as comprehensive as what you're looking for, the Open311 GeoReport API standard does cover a wide range of forms for service request transactions with city governments. Currently, this is primarily focused on location specific things in public space, like a form to request that a broken streetlight gets repaired, but some Open311 APIs are also starting to include location-agnostic forms that are more targeted at the needs of an individual. Since the Open311 API allows for a lot of flexibility in publishing and receiving custom forms it may get even wider use as a standard way to make this available in a machine readable format. You can see a list of city Open311 endpoints at http://wiki.open311.org/GeoReport_v2/Servers and an aggregate list of the forms that are managed by these APIs at https://scraperwiki.com/scrapers/open311_services/