Command-` does this natively: cycle through windows of the active application. Note that on an ANSI keyboard backtick is right above Tab so it makes sense from a layout perspective.
option+< and option+> to resize window to left and right, and option+p to maximize. And also control+j and control+k to switch tabs in browsers and terminals.
Probably there are also native shortcuts for that, but I like how I can make mines consistent across all apps.