digitalWrite(LED,!LED);

Forum 2005-2010 (read only) General Frequently-Asked Questions
5

You could do this:
digitalWrite(led1Pin, led1State = led1State ? LOW : HIGH));
digitalWrite(led2Pin, led2State = led2State ? LOW : HIGH);

or have a function that inverted the value:

uint8_t invert( uint8_t value){
// returns LOW if the given value is HIGH, else HIGH if the given value is LOW
if( value == LOW)
return HIGH;
else
return LOW;
}

led1State = invert(led1State);
digitalWrite(led1Pin, led1State);

Note that the invert function does that same as same as:
value = value ? LOW : HIGH;