I have been converted!

To shooting raw. I tried shooting and processing in raw when I first started out with my rebel but didnt like it. I tried it again yesterday. 20d set to raw plus jpeg. I did some snapshots in really mixed lighting. It was sooooo easy to fix the white balance! From now on I will shoot all my indoor shots in raw.

I agree that RAW is best... but if you want a trick for JPEG... why don't you use the custom white balance feature.

Get a plain white piece of paper.
Hold it up in front of your subject so it captures the same light (same angle).
Switch your lens to MF and take a shot so the white paper fills the frame. Use MF so the lens doesn't hunt. It doesn't have to be in focus.
Then, in your menu (for 20D I think it's the option at the bottom of the first screen in the menu) pick custom white balance.
Then it'll default to the last picture you took, which will be the paper.
Click Set to set that picture as the white balance.
You may get a warning to switch your white balance to custom... so switch you white balance (in the menu) from AutoWB to Custom (two ramps with a ball in the middle).

Now take more pictures and your balance will be corrected.
It's cool.. if your pictures were coming out orange... when you take a shot of the paper, it'll look orange. The camera analyzes this picture and makes the appropriate adjustments... so it would add the opposite colour to cancel it out.
You can delete the image once you set the white balance... it just uses the image to set the custom WB settings (temperature and tone).

I often do a custom white balance when shooting something formal. But for instance with my grandaughter she doesnt sit still under one light source for very long and runs from room to room. There is not always the opportunity to do a custom white balance.
Also, I have found that even custome WB is not all that accurate if you have a lot of mixed lighting going on with the flash.

I found with a flash, setting WB to "flash" works well in all lighting situations.
If it's off, I just use a curves layer to manually correct each colour channel.