from http://carlsonmfg.com/industrial-resources-articles/18-cnc-code-programming

G00 Rapid Transverse Motion
G01 Motion by a feed rate
G02 Motion in an arc clockwise
G03 Motion in an arc counter clockwise
G04 Dwell
G17 XY Plane selection
G18 XZ Plane selection
G19 YZ Plane selection
G28 Return to Machine zero for axis selected
G40 Cutter compensation Cancel
G41 2D Cutter compensation Left
G42 2D Cutter compensation Right
G43 Tool length compensation + (add to tool length offset)
G44 Tool length compensation – (subtract tool length offset)
G49 Cancels G43 G44
G50 Sets a speed limit for Constant surface speed (lathe)
G52 Set Work Coordinate system
G54 Work coordinate system #1
G55 Work coordinate system #2
G56 Work coordinate system #3
G57 Work coordinate system #4
G58 Work coordinate system #5
G59 Work coordinate system #6
G65 Macro Subroutine call
G70 Bolt Hole Circle
G71 Holt Hole Arc
G72 Bolt holes along an Angle
G73 High Speed Peck Drilling
G74 Reverse Tapping
G80 Turns off all canned cycles
G81 Drilling
G82 Spot Drilling
G83 Peck drilling
G84 Tapping cycle
G90 Calls up an absolute Co-ordinate grid system Positioning
G91 Calls up an incremental Co-ordinate grid system Positioning
G92 Set Work Coordinate system shift value -(grid shift)
G94 Feed per minute mode
G95 Feed per spindle revolution mode
G96 turns on Constant Surface Speed (lathe)
G97 Turns off Constant Surface Speed (lathe)
G98 Canned cycle initial point return
G99 Canned cycle R Plande return

M00 Program stop - Tells the CNC machine to stop in the middle of a program.
M01 Optional Program Stop - Tells the CNC machine to stop ONLY if the optional stop switch is active
M02 Program end
M03 Turns the Spindle on in a Clockwise direction
M04 Turns the Spindle on in a Counter-Clockwise direction
M05 Turns the Spindle off
M06 Tool change
M07 Optional coolant is not available on all machine configurations
M08 Turns flood coolant on
M09 Turns flood coolant off
M10 Normally used to turn 4th Axis brake on (mill)
M11 Normally used to turn 4th Axis brake off (mill)
M19 Spindle Orientation
M30 Program end and reset
M31 Chip conveyor on (forward)
M33 Chip conveyor off
M88 Turns through the spindle coolant on
M89 Turns through the spindle coolant off
M97 Calls up sub program for local program
M98 Sub Program Call
M99 Loop or return to rerun a sub program

// canonical functions
// p44/52 of http://www.nist.gov/customcf/get_pdf.cfm?pub_id=823374

SET_ORIGIN_OFFSETS(double x, double y, double z, double a, double b, double c)
USE_LENGTH_UNITS(CANON_UNITS units)
STRAIGHT_TRAVERSE(double x, double y, double z, double a, double b, double c)
SELECT_PLANE(CANON_PLANE plane)
SET_FEED_RATE(double rate)
SET_FEED_REFERENCE(CANON_FEED_REFERENCE reference)
SET_MOTION_CONTROL_MODE(CANON_MOTION_MODE mode)
START_SPEED_FEED_SYNCH()
STOP_SPEED_FEED_SYNCH()
ARC_FEED(double first_end, double second_end, double first_axis, double
    second_axis, int rotation, double axis_end_point, double a, double b, double c)
DWELL(double seconds)
STRAIGHT_FEED(double x, double y, double z, double a, double b, double c)
STRAIGHT_PROBE(double x, double y, double z, double a, double b, double c)
ORIENT_SPINDLE(double orientation, CANON_DIRECTION direction)
SET_SPINDLE_SPEED(double r)
START_SPINDLE_CLOCKWISE()
START_SPINDLE_COUNTERCLOCKWISE()
STOP_SPINDLE_TURNING()
CHANGE_TOOL(int slot)
SELECT_TOOL(int i)
USE_TOOL_LENGTH_OFFSET(double offset)
COMMENT(char * s)
DISABLE_FEED_OVERRIDE()
DISABLE_SPEED_OVERRIDE()
ENABLE_FEED_OVERRIDE()
ENABLE_SPEED_OVERRIDE()
FLOOD_OFF()
FLOOD_ON()
INIT_CANON()
MESSAGE(char * s)
MIST_OFF()
MIST_ON()
PALLET_SHUTTLE()
OPTIONAL_PROGRAM_STOP()
PROGRAM_END()
PROGRAM_STOP()