PSA or Piedmont have CLT. 7-8 flights /day. Endeavor has ATL. 8-9 flights /day. Envoy you could go to MIA or DFW and they have 4 flights /day. DCA is doable with 4 flights /day if PSA or RAH interest you there. RAH and XJT also have an IAH base and I think there are 4-5 flights /day there too.

...my personal opinion CLT or ATL are your best bet with DCA a distant 2nd. Endeavor or PSA is who your choice will likely come down to.