Hey,  
        I am building a new gaming-computer, i have chosen the parts and they are as follows:
 
Motherboard: EVGA nForce 680i SLI SKT775 7.1channel audio DDR2 ATX Motherboard
 
CPU: Intel Quad-Core Q6600 G0 Stepping 2.4Ghz
 
GPU: XFX 8800GT XXX Alpha Dog Edition 670mhz, Memory Clock Speed 1.95Ghz, 512mb
 
Case: Antec Nine Hundred Gaming Case
 
RAM: 4GB OCZ PC2-6400, 800Mhz
 
PSU: CoolerMaster 620W REAL POWER MODULAR PSU
 
CPU Cooler: IFX-14 or TRUE (Unsure, still deciding)
 
Fan speed Controller: Sunbeam Chromatic Windmill
 
This is my computer setup but i am still not sure about the PSU? Can 620w Be enough to power the CPU GPU and all other components? As i do know that the 8800GT's are very power hungry? Taking in mind of the other components i.e. WiFi card, Internal Bluetooth, Optical Drives (2 of them), Media Card reader/writer, Sound card...etc... All of this can be powered by a 620w? Also looking out for the future, if i do upgrade? i.e. RAM.. Is 800w a good choice, won't it really hit the electricity bill, if left on over night?
 
I'm very sorry for so many questions. Thank you.

EDIT: I saw the 700w CoolerMaster Real Power Modular PSU and its only a 8 quid more from the 620w? Shall i be on the safe side and get the 700w?

my set up:  
Gigabyte p965 ds3
X3210 oc to 3.4 Ghz
8800 gts 640 MB video card.
1 74 GB raptor
1 500 GB samsung HD
corsai 520W
Using "kill a watt" to check the power usage from wall
stand by mode: 180 w
prime 95: 200w
3dmark 06: 260W
so you get my point, buy a power supply has highest current on 12 volts rail and do not worry about the total wattage.

Highest current on a 12v rail? SOrry im a bit newbie! What is a rail? Is it that "Wires" which connect into each component?  
 
Sorry that answer is a bit confusing...how do i know which is good for my setup @_@!  
 
Can someone do a quick check to see if the "CoolerMaster 700w REAL POWER" PSU is good for my setup, link :
 
http://www.dabs.com/productview.as [...] ationKey=0

Get this one  
http://www.dabs.com/productview.as [...] 1259,50113

Hmm... can you explain why? (sorry if it sounds rude)

Hey, anything above a "GOOD" 400W power supply will work.
 
But, for your concern: The CoolerMaster 700W is plenty.
 
Here's a good one as well.
 
http://www.dabs.com/productview.as [...] nKey=11259
 

 
YES! That is plenty of power.  I have a similar setup with with a more power hungry 8800 GTX and I have a 550 Watt PSU and I only draw ~340 watts from the wall at full load and I overclocked my system to 3.3GHz.

Wow! 550w powering a GTX and OC'd! Woo...thats helped me out, thanx a bunch peeps