Based on either seeing references to this on the SD stations or some internet information (which may or may not be accurate) I believe the following are available in HD and would like to see them added to the FiOS lineup here (Fitchburg, MA) if possible:
Local Station: PBS - WENH - TV 11 HD (New Hampshire Public Television)
C-SPAN 2 HD
C-SPAN 3 HD
NECN HD (New England Cable News)
There are others like BBC America HD, FUNimation HD, etc... but they have already been mentioned in other posts.