At RDU some of the biggies are:
Spectracor-GIV
General Parts-BE400/Hawker 800/Citation X
SAS Institute-Hawker 400/Citation X/BBJ/Falcon 900
Martin Marrietta Materials-Citation XL
State of NC-Citation/King Air/Conquest
Progress Energy-Citation XL?
If you find you need to bridgethe gap between 121 and 91, you might check out Jet Logistics at RDU or Landmark's charter dept at INT (they have aircraft based at RDU, though I dont know if these are crewed by Landmark or the owners). Another option to look at might be Citation Shares, since they have a domicile at GSO.
Sorry I dont have contact info for any of these, but if you hang around Landmark and Southern Jet for a few days you might get some info. Lots of others there too if you hang out and play 'meet and greet'.
Good Luck!