There's a lot of new ones in win7 that I find very useful, in addition to some that has been around for a while:
Win+arrow keys* moves the active window around. Try it! Win+up maximizes, win+left and right moves the window to the left and the right, and win+down restores it down (makes it smaller) if the window is maximized, and minimizes it if not.
LTK mentioned win+d for desktop.
Win+l locks the screen, which is really practical if you need to leave your computer somewhere public (library, work, etc.).
Pressing and releasing
win opens up the start menu as it always has(okay, at least for as long as I have been using a computer). In win7, you can start typing right after doing this, and what you type goes into the search bar. This is very useful! If I want to start chrome now, I pres win, type 'ch', and press enter, and windows starts the program, without me ever having to navigate any menu whatsoever.
f2 allows you to rename a file or folder! Just select it in the windows GUI, and press f2, type in the new name, and press enter when done.
There's also a couple of useful keyboard shorcuts in all of the modern internet browsers that's pretty damn cool:
ctrl+l moves the cursor to the menu bar, and highlights all of it.
alt+d does the same!
crtl+t opens a new tab.
ctrl+tab cycles through your open tabs, just like alt+tab does for open programs.
ctrl+shift+tab does the same, just backwards instead of forewards.
for chrome specifically:
ctrl+j opens the downloads screen.
ctrl+w closes the open tab.
EDIT:
I remembered more about windows and browsers!
in the windows folder view,
alt+up brings you one level up in the folder hierarchy.
in a web browser,
alt+left and
right goes backwards and forwards in your history. Very useful if you are trying to go back, but backspace won't work since you are in a textfield.
/EDIT
Using keyboard shortcuts makes you a lot less prone to wrist problems due to mouse use. You should do it! It's also effective to learn and use the shortcuts that's available for all of the text editors you meet - ms office, open office, even the QC forums posting thingy! Try it now! With practice, you'll do things better and faster.
Ctrl+left and
right moves you to the start or end of the word your cursor** is at!
ctrl+backspace and
delete removes a whole word instead of just a letter!
ctrl+up and
down does different things, either it moves the cursor to the start or end of the current paragraph, or it scrolls the screen without moving the cursor. Depends on the program.
*for you less savvy out there, with Win I mean the button between the left ctrl and the left alt, with the windows symbol on it. If you have an keyboard made for hippies or hipsters, it will be labeled something else.
** uh, the thingy that indicates where you are writing. It has a fancy word that I can't come up with. Not the mouse cursor.
The more I learn programming, the more I realize how important shortcuts are. Whenever I find myself doing something with the mouse a lot, I google for a keyboard shortcut. It's usually around, programmers love them, and after all, it's programmers that makes the programs with the keyboard shortcuts in the first place.
EDITEDIT:
http://en.wikipedia.org/wiki/Table_of_keyboard_shortcuts
