Hi Carl,
I had a modded 30D (had - someone stole it...). It had the internal filter replaced with a clear filter, so it was also very sensitive to IR and UV. If you want to do 'normal' photography and want accurate colour, you need to not only do a custom white balance, but also use a UV/IR blocking filter. I used B+W 486 and 489 filters - but they are stupidly expensive.
http://www.mainlinephoto.com.au/category7_1.htm
http://www.filtershop.com.au/schneider/
You can also use insert filters, which means that you only need one filter, not one for each lens. But you can only use these filters with EF lenses, not EF-S lenses.
http://www.teleskop-express.de/shop/...ml/filter_id/2
Somewhere I have a post with a lot of test images showing the effects of no filter, filter and various white balance settings.
If you are only going to use the camera for astro and/or IR or UV, then you don't need any colour-correcting filter. If you are only doing astro, then you don't even need the internal (clear) filter - but you'll have to focus manually and be careful of dust on the sensor.