ISO : The lower the sensitivity, the finer the grain, but more light is needed. This is excellent for outdoor photography, but for low-light conditions or action photography (where fast shutterspeeds are needed), more sensitive or "fast" film is used which is more "grainy"

Aperture: Aperture is also known as 'f-stop' and you can think of it as being similar to the pupils in your eyes

Shutter speed: Shutter speed is how long the sensor in your camera is exposed to light

Sensor size: The three most common sensor sizes are full frame (the sensor is the same size as a frame of 35mm film), APS-C (is by far the most common format) and Four-thirds

Type of lenses

• Wide angle: 28mm or less, good for interiors and landscapes
• Standard: from 35mm and 85mm, good for general use and portraits
• Telephoto: from 100mm to 300mm, good for sports, portraits and wildlife

Battery Grip

For the 450D, here are the options:

• Canon BG-E5: Which is the canon version. On some US sites, you can find it with a LCD display
• Flashpoint Professional Battery Grip: http://www.adorama.com/ICABGE5AP.html∞
• Opteka Battery Grip: The wheel seems to feel differently than the Canon one

Wireless Remote Release

Flash

I will need an external pack to use the flash remotely.

Tripod

You can buy the body and the head separately

Manfrotto

Camera bag

Camera strap

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References:
http://www.dpreview.com/∞
http://www.knowyourdslr.com/dslrbasics/startersguides/12708/dslr_starters_guides_aperture.html∞