Cmd ⌘ `
Cmd ⌘ Shift ⇧ ` to go the other way.
Left of z on a UK keyboard [non-shifted ~ ]
BTW, specifically in Chrome, but no other app I know of on Mac, Cmd ⌘ (number) will select individual tabs on the frontmost window.
Update:
Since first adding this answer, Cmd ⌘ (number) has been added to Safari, from I think v9.
It also would appear that Cmd ⌘ ` is yet another of those language-specific shortcuts; so if anyone finds any more variants, please specify for which language & keyboard type.
Further info:
You can change the keys in System Prefs > Keyboard > Shortcuts > Keyboard...
though it doesn't list the reverse direction, it does still work when you add shift to that new combo. I tested by moving mine from ` (and ~ ) to § (and ± )