MenuAndDockless is a SIMBL plugin for OS X 10.6 or later, enabling you to choose for every native (!!!!) Cocoa application whether it should appear in the menu bar and Dock or not. In addition, you can save the default window size and position--which also works for multiple-display setups--automatically adjust window sizes, center and arrange windows, and toggle fullscreen mode individually for each application by customizable shortcuts or menu items.
On smaller screens (on an 11" MacBook Air, for example), this often makes a great deal of sense because you gain a lot more free 'space', and it reduces possible distractions because you don't have to manually position windows again -- one keystroke or click and the window will be adjusted and positioned as you intended.
And because Finder is now also written in Cocoa, MenuAndDockless even works for Finder (just needs to be restarted once).
MenuAndDockless is free and works on every Mac with a 64-bit processor running OS X 10.6 Snow Leopard or later, and is not a hack like other tools -- it's just an addition, and will not cause any trouble.