Try the ones you can afford, take the one that's the most comfortable to use.
Yes the 400D is a great camera. But so are just about every other DSLR available on the market today. If spot-metering is important to you, skip the 400D/450D/1000D - they don't have it. If you want both spot-metering and Canon, get the 40D - but that's way more money. If brand is not the ultimate consideration for you, but spot-metering and money is, look at the Nikon D40 and Pentax K100D Super. They're both great camers, they both have spot-metering, and they're both selling for peanuts.