While iOS doesn't enjoy public code-names like OS X - no Snow Leopard or Mountain Lion - they do use internal code names, typically derived from ski resorts. Here a list of previous, current, and future iOS code-names.

  • 1.0: Alpine (1.0.0 - 1.0.2: Heavenly)
  • 1.1: Little Bear (1.1.1: Snowbird, 1.1.2: Oktoberfest)
  • 2.0: Big Bear
  • 2.1: Sugarbowl
  • 2.2: Timberline
  • 3.0: Kirkwood
  • 3.1: Northstar
  • 3.2: Wildcat (iPad only)
  • 4.0: Apex
  • 4.1: Baker
  • 4.2: Jasper (4.2.5 - 4.2.10: Phoenix)
  • 4.3: Durango
  • 5.0: Telluride
  • 5.1: Hoodoo
  • 6.0: Sundance
  • 6.1: Brighton
  • 7.0: Innsbruck
  • 7.1: Sochi
  • 8.0: Okemo
  • 8.1: OkemoTaos
  • 8.2: OkemoZurs
  • 8.3: Stowe
  • 8.4: Copper
  • 9.0: Monarch

We'll update as new versions are released or otherwise become known.

Sources: @stroughtonsmith, iPhone Wiki, @markgurman