Whatever you buy will be superseded in about 18 months, but will still be just as good as it ever was!
The 30D is a great camera. Maybe the 40D will be better - we'll have to wait for the reviews. But in terms of allowing you to take good pics, there is absolutely nothing wrong with the 30D. If you can get one for that sort of price, you can't really go wrong. (But beware of bad retailers - if it's too good to be true and all that.

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The 300D batteries will work fine in the 30D. The BP511 and BP511A are the same physical size and voltage, but the latter can hold slightly more charge. Many third-party batteries had a higher capacity than Canon's BP511.