Fellow digiphoto buffs..

Took the plunge and bought the 20D. Got the kit w/18-55mm lenses.

Now I need some advice to buy lenses to really start using the camera. As many of you have the camera and have lenses/Flash, please suggest:

>2-3 Wide Angle Lens combo (28-135, 70-300, etc.) ~ $500 to $600
>Focal lense enhancers (1.4X or 2.0 X), many brands, which works?
>Lenses maker (I have seen Sigma, Tamron, Canon, etc.)
>Is the new Canon lenses with IS worth buying (steep Prices)
>What is the best flash to use for this camera (best price/non canon)
>Places/Links where I can buy

There are many links for camera price comparisios, I could not find the same kind of setup for lenses/flash/accessories for Canon. Maybe I am not looking at the right place and someone can guide me in the correct direction.