Used

Skybox Name Map Credit Total
morning morning Crossover 2 Valve 1
desert desert Boot Camp · Crossfire* · Datacore* · Frenzy* · Hunted · Lambda Bunker* · Push* · Rapidcore* · Snark Pit · Subtransit Valve 4
10*
dusk dusk 2 Fortresses Valve 1
night night Avanti · Canalzone 2 · Eleventh · Gasworks · Ravelin · The Rock · Stalkyard · Undertow · The Well Valve 9
2desert 2desert Bounce Valve 1
dustbowl dustbowl Badlands · Casbah · Dustbowl · Epicenter · Flagrun · Warpath Valve 6
water water Monkeypox Valve 1
city2 city2 The Signal Valve 1

*This map doesn't have a skybox, but the game loads by default this one (also if you load a map with a different skybox and change back to this, it will keep the skybox from the last map).

Cut / Unused

Skybox Name Map Credit Total
avanti avanti --- Valve 0
arctic arctic --- Valve 0

Note: The ones in bold are the first ones to use that skybox.