You can just hold the shutter button half way after you've achieved focus and push the flash down. If you want it off for all of your pictures, refer to page 52 or 53 of your owner's manual to totally disable the flash. If you're shooting in auto mode, though, I would recommend trusting your system and letting the flash fire for some fill on your subject. If you prefer the look of more natural light (like I do), you really need to learn how to shoot out of auto mode...
Jack of all trades, master of none...
5D / 40D / 10-22 EF-S / 50 1.4 / 24-105 F4 L IS / 70-200 2.8 L IS / 60 EF-S Macro / Quantum T5D-R / Turbo 2x2 / CB Digital Pro-M / QTTL Wireless adapter / memory, etc...