The A321T subfleet used for JFK-LAX/SFO is the only domestic routing and domestic fleet with planned full-time lie flat seating.
However, internationally configured planes (more and more of which are either being delivered or retrofit with lie-flat seating) sometimes run select domestic flights (often hub-hub, e.g. MIA-LAX) for either positioning, utilization, or training purposes.
Currently, the US A330 fleet has lie-flat. In addition the AA 77W (not used domestically currently AFAIK) and AA 787 (will do DFW-ORD turns in May) have lie-flat.
And the AA 772 fleet, 763 fleet (those planes which aren't being retired), and 75L (note this is the subfleet used for international flying, not all of the 757s) are, to the best of my knowledge, being (slowly) retrofit with lie-flat. Not sure about current progress, but I think it's more miss than hit with these types right now.
I'm not sure about the US international 757s but expect they are also in for retrofit at some point? Someone else can hopefully confirm.