In the propellor era, there were lots of impressive milk runs, many of them serving airports not capable of accepting jets. What about domestic U.S. milkruns in the jet age? Here are a couple that come to mind:
NW 109: EWR-PHL-CLE-ORD-MSP-JMS-BIS-BIL-HLN-MSO-GEG-PDX-SEA Flown with 727-200
NA 492: MSY-MOB-PNS-PFN-TLH-JAX-ORF-DCA-BAL-JFK Flown with 727-200
RW 706: BUR-LAS-SLC-TWF-BOI-LWS-PSC-YKM-SEA Flown with DC-9-10
TI 905: MSY-BTR-LFT-IAH-DFW-MAF-ABQ-LAX Flown with DC-9-10