[Mikuro]

The first thing switchers (or potential switchers) should learn is that that the Dock is not the task bar, and should not be considered an equivalent at all. They're superficially similar, but they really serve different purposes.

Like Ora said, there's Exposé and command-tab ("apple" key = command). There's also a user-definable shortcut for cycling through windows of the active app (by default it's command-`). Also, all applications should have a "Window" menu that lets you switch between windows.