Do you mean...
1) Programs that are running but hidden (e.g. you hid the window using Apple-H)
2) Programs that are running but have no open window (e.g. you are running Safari and you close all the windows)
3) Programs that are running but minimized (you clicked the minimize button in the upper left, and it went into a little iconified version in the lower right of the dock)
4) Programs that are not running at all (e.g. they have no windows, no black triangle under them, etc)
I guess the answer depends...
For (1) it should unhide them when you apple-tab.
For (2) once you apple-tab to the program, you can use apple-n typically to get a window.
For (3) this behavior is somewhat dependent on the application. A lot of them do unminimize, but I think there are some that do not.
For (4) no, there is no effective way to do this. If you want alternative ways to launch programs, look at things like Quicksilver, using Spotlight, etc.