[blackstar]

I have always wanted to be able to use the keyboard more on OS X to switch between applications and for other uses. The introduction of spaces in Leopard has helped a lot with it. Now I can switch between the apps I use with ctrl + 1, 2, 3, 4.
Other shortcuts I use in OS X are more Word / Text editing related.
cmd + B = bold
cmd + I = italic
cmd + u = underline
cmd + e (l, r) = center alignment (left, right)

Post some of the keyboard shortcuts that you use a lot...

[seanc]

cmd + p = print
cmd + c = copy
cmd + v = paste
cmd + x = cut
cmd + z = undo
cmd + y = repeat (in Office)
cmd + q = quit
cmd + r = refresh
cmd + ` (or ~) = switch windows within an application (very useful in Office, except when it breaks)

[Sage]

I probably use cmd+tab and cmd+{/} the most.

[richwig83]

cmd + w = close window
cmd + a = select all
alt + cmd + esc = force quit apps
fn + cmd + esc = Front-row
cmd + click link in safari = open in new tab (must use it about 100 times a day)

also ive only just discovered the beauty of spotlight... so easy to search for apps/docs or do a quick sum without loading calc!

[blackstar]

I have added the open in new tab to my 3rd mouse button.

what is

I probably use cmd+tab and cmd+{/} the most.

for?

[Sage]

cmd+tab switches between apps (hold down the cmd key, then tap on the tab key; hold shift to go in reverse).

cmd+{ and cmd+} switches between tabs in Safari.

[blackstar]

oh ok.
I have used cmd+shift-left&right arrow to switch between tabs.

[Hal Itosis]

These can be fun:
Default Mac OS X System Key Bindings
Customize the Cocoa text binding system

[Salty]

If there's a keyboard shortcut for it, I do it. I basically use the menu bar to find out what my hot keys are