I am working on a way to put my arduino into stand by mode. is there a way to turn off the 5v pin on the arduino, so im not wasting energy going through my circuit?
If I understand your question, the answer is NO.
If you to "turn off" the 5V rail, you must turn off the Vin.
Not any way built into the Arduino since the 5V comes from the USB or regulator, not from the processor..
Some peripherals have a low-power standby mode you can use.
Some peripherals use so little power (<20 mA) that they can be powered by a digital output pin.
Much depends on what devices you are connecting to the Arduino.
If you are very concerned about power you will want to run at a low voltage and low speed. The voltage regulator, USB interface,and the LEDs take a significant amount of power so you will probably want to use a "bare-bones" board..
The Atmel chip (the microcontroller) uses almost no power in sleep mode.
You can make a barebones Arduino-compatible board running 1 or 2 years on three AA batteries.
Can you tell us what you use to power it ? and should someone push a button to wake it up ?
You could power your external circuitry via a transistor and simply switch that on or off as you come in or out of sleep mode.