After the announced IAH Centurion Lounge here's an updated list:
significant airside access (you can walk to mostly any gate from any other gate without having to re-clear security),
somewhat limited airside access (you can walk to some gates but not the majority of gates, without having to re-clear security), and
limited airside access where you cannot walk from one gate to the majority of other gates without having to re-clear security.
I have noted if there's an existing DL hub with multiple SkyClubs and crossed out locations that already have an AX lounge.
mia has also noted the presence of Priority Pass (P) and Airspace (A) lounges:
1. ATL - 46.6; DL hub + SkyClubs P=1
2. LAX - 34.3 P=4
3. DFW - 34.2 P=1
4. ORD - 33.6 P=2
5. JFK - 26.2 P=2, A=1
6. DEN - 26.0 P=0
7. SFO - 22.7 P=0
8. CLT - 21.5 P=0
9. LAS - 20.5 P=2
10. PHX - 20.3 P=1
11. IAH - 19.7 P=1
12. MIA - 19.4 P=2
13. SEA - 17.8 P=3
14. EWR - 17.6 P=1
15. MCO - 17.2 P=0
16. MSP - 16.9; DL hub + SkyClubs P=0
17. DTW - 15.7; DL hub + SkyClubs P=0
18. BOS - 15.4 P=1
19. PHL - 14.7 P=0
20. LGA - 13.4 P=1
26. DCA - 10.0 P=0