First look at Windows 7's User Interface

They're also found on the Start Menu.

The biggest visible result of all this is the taskbar. The taskbar in Windows 7 is worlds apart from the taskbar.

Text descriptions on the buttons are gone, in favor of big icons. The icons can—finally—be rearranged; no longer will restarting an application put all your taskbar icons in the wrong order. The navigation between windows is now two-level; mousing over an icon shows a set of window thumbnails, and clicking the thumbnail switches windows. Right clicking the icons shows a new UI device that Microsoft calls "Jump Lists."

Jump lists provide quick access to application features. Applications that use the system API for their Most Recently Used list (the list of recently-used filenames that many apps have in their File menus) will automatically acquire a Jump List containing their most recently used files. There's also an API to allow applications to add custom entries; Media Player, for example, includes special options to control playback.
This automatic support for new features is a result of deliberate effort on Microsoft's part. The company wants existing applications to benefit from as many of the 7 features as they can without any developer effort. New applications can extend this automatic support through new APIs to further enrich the user experience. The taskbar thumbnails are another example of this approach. All applications get thumbnails, but applications with explicit support for 7 will be able to add thumbnails on a finer-grained basis. IE8, for instance, has a thumbnail per tab (rather than per window).
Window management has also undergone changes. In recognition of the fact that people tend only to use one or two windows concurrently, 7 makes organizing windows quicker and easier. Dragging a window to the top of the screen maximizes it automatically; dragging it off the top of the screen restores it. Dragging a window to the left or right edge of the screen resizes the window so that it takes 50% of the screen. With this, a pair of windows can be quickly docked to each screen edge to facilitate interaction between them.
Another common task that 7 improves is "peeking" at windows; switching to a window briefly just to read something within the window but not actually interact with the window. To make this easier, scrubbing the mouse over the taskbar thumbnails will turn every window except the one being pointed at into a glass outline; moving the mouse away will reinstate all the glass windows. As well as being used for peeking at windows, you can also peek at the desktop:

Peeking at the desktop is particularly significant, because the desktop is now where gadgets live. Because people are increasingly using laptops, taking up a big chunk of space for the sidebar isn't really viable; Microsoft has responded by scrapping the sidebar and putting the gadgets onto the desktop itself. Gadgets are supposed to provide at-a-glance information; peeking at the desktop, therefore, becomes essential for using gadgets

The taskbar's system tray has also been improved. A common complaint about the tray is that it fills with useless icons and annoying notifications. With 7, the tray is now owned entirely by the user. By default, new tray icons are hidden and invisible; the icons are only displayed if explicitly enabled. The icons themselves have also been streamlined to make common tasks (such as switching wireless networks) easier and faster.