These are the iTunes keyboard shortcuts that you'll have the most fun with:
Command l
toggles between Show Player and Hide Player
Command T
toggles Visuals on and off
Command F
toggles Visualizer full-screen mode on and off
Command DownArrow
turns the volume down
Command UpArrow
turns the volume up
LeftArrow
first tap selects the beginning of the current song; second tap selects the previous song
RightArrow
selects the next song
Option Command DownArrow
mutes the sound
Spacebar
toggles between Pause and Play
Other keyboard shortcuts:
Command N
creates a new playlist
Shift Command N
creates a new playlist from the highlighted songs (not the songs that are checked)
Command A
selects all songs in the current song list
Shift Command A
deselects all songs in the current song list
Command R
shows current song file in the Finder
Command E
ejects a CD
Command M
minimizes Player window to the Dock
Command ?
launches iTunes Help
Command Q
quits iTunes
Visualizer shortcuts:
R
changes Visualizer to a new random set of visual effects
M
cycles through Visualizer modes
N
toggles between Normal and High Contrast colors
D
resets Visualizer to the default settings
I
Displays song information
F
toggles Frame Rate Display on and off
B
displays the Apple logo briefly when Visuals are turned on