The USGS Center for Integrated Data Analytics - cida.usgs.gov - created this prototype in Summer 2010 for The National Map Viewer Framework in OpenLayers. It calls WMS or Tiled services, in similar style to TNM.
To use, extract the attached zip, and double-click index.html.
This is a seeder starter OpenLayers prototype to anyone else who wants to download the code and modify. Maybe could go on "github".
Recommended future modifications:
// #1 Re-architect so uses http://viewer.nationalmap.gov/viewer/js/config/default.json - so this won't have to be maintained at all
// #2 Re-architect so layers are build from inspecting the service
// To-do - Handle Transparency, Service Layer Order, Metadata URLs, bookmark zoom/aoi/layers
// Handle Zoom starting points
(See attached zip - \assets\js folder for customizing the URLs - really could be any map service).