I have an external power supply DC 9V 600mA. It is ok to use it on Arduino? The recommended maximum input voltage is 12V, what is the recommend maximum input current?
Yes, that should be a good match for your Arduino.
There is no maximum current rating for the power supply connected to Arduino, the Arduino will draw as much current as it needs (and the voltage regulator can cope with). But you should be good to go with that 9v 600ma supply.
thanks mem!
ou, em português, obrigado (i put this post in the wrong forum .-)
Can i use a 7.4V 800mAh power supply with the Arduino Mega?
Yes.
The recommended minimum input voltage is 7V.
Ok, thanks 
Was worried about the current..
Would an extreme 12V, 4.5A power source be ok or would the onboard arduino voltage regulator fry?
The voltage regulator probably will explode if your circuit drains 4.5 A.
But if the source is 12V/4.5A, doesn't mean that this current will flow in the circuit, it's only the maximun current that the source supports.