Canon 40D vs Rebel XSI

I am looking into buying my first digital SLR camera and I have narrowed it down to the 40D or XSI. I just can't decide which one. Canon is offering a spectacular rebate right now that ends January 17. I have found the Rebel XSI with the 18-55mm lens and the 55-250mm lens for $789.95, an awesome deal. I have also found the 40D with the 28-135mm lens for $979.95. Each has their pros and cons, and I just want someone's opinion about which camera would be the best bet for me. I am currently taking photography classes and I really want to get serious about it. This camera has to last me awhile too. Thanks in advance for your help!