If nothing from either camera jumps out and grabs you, yelling "Buy me, you need me!!!", you may not be quite ready to move up. The shelf life of any model is relatively short, and it may be wise to hold off until the next generation unless you really NEED to buy now.

The difference between 6.2MP and 8.2MP is barely noticeable, so that would not be reason to go for the 30D. On the other hand, the difference between 8.2MP and 10.2MP is even less noticeable, so that would not be a compelling argument for the XTi over the 30D.

The 30D is a little bit more sophisticated in its features compared to the XTi. Only you could decide if they would actually make a practical difference to your photography. It is also heavier which may or may not be good.

Either one would be a slight upgrade from what you now have, but if you can not find a compelling reason to buy one or the other, wisdom would say hold off until a unit comes on the market with obvious advantages.

Unless you use your camera a great deal more than most enthusiasts, there is no compelling reason to opt for the 30D over the XTi, and for most enthusiasts who just shoot occasionally and don't records hundreds of exposures in one day, the stronger body and more robust construction, as well as a few advanced features do not outweigh the advantage almost twice the resolution will provide over your 6.2 Rebel. The Rebel XTi for most enthusiasts is a lot more of what you are likely to use for less money.

That's the rationalists practical perspective. But the 30D may seem attractive like a Cadillac is more attractive than a Chevrolet. it provides a larger ego boost, although its really just a gussied up version of the same basic chassis.