If you're gonna buy from the well known high street store that is offering the half price tamron lens, make them price match

the 30D price is way OTT, can be had for a good £100 cheaper online, and they will match it.
i'd say the 400D isnt that much worse than the D80 especially considering the cost, you're paying for the lens more than anything else. I do believe the d80 is more 400D level than 30D level, as 30D with the same "equiv" lens is over a grand. The d200 is more 30D level, and the 5D doesnt have any competition at all from nikon.
Nikon are quite clever with their pricing though, they always make sure that their cameras fit between the canons, so that arguements like are happening in this thread will always go on
As far as entry level SLRs go, the 400D is the best of the bunch IMO. That with the Tamron 75-300 lens for £100 will get you started nicely, very good starter kit thatll let you see what you use, and then when you find what you're lacking lens wise you've got a lot better lens choice in the mid range with canon equipment (the F4 L range for example, 70-200 F4L <£500, 17-40 F4L <£500) vs the Nikon range.
If you can afford it though, the 30D is obviously a better camera. I have a 20D and a 30D, and they are just that bit nicer to use
At the end of the day though, no matter what camera you buy from the latest sub £1k offerings (400D, D80, 30D, D200) you're not gonna get a bad camera, so don't worry TOO much
Tom.