Mac only: If you have an especially large monitor, multiple monitors or are just used to the Windows way of doing things, free app MenuEverywhere makes the menu bar drop-down menus accessible from any window on the desktop.
While previously mentioned SecondBar certainly makes the menu bar a bit more accessible to multi-monitor users, MenuEverywhere takes it a step further by putting it at the top of every window (without taking up any extra space). Just move your mouse above the left-hand side of the window (above the "traffic lights") and a menu will appear, with all the usual menu bar drop-downs for that application. You can also access MenuEverywhere with a hotkey, if you're more of a keyboard shortcut fanatic. Check out the video for a demonstration and hit the link to check it out.
MenuEverywhere is free as nagware, costs $US7 for the nag-free version and is for Mac OS X only.