What's the difference between the Canon Rebel T2i and T3i? I thought the T3i was just the upgraded verson of the t2i, but now DH is seeing the 3 cheaper than 2. Any recommendations for one over the other? And I want the 2i or 3i, not 2 or 3 without the i, right?

This will be my first DSLR, I want to take good pictures on vacation and of my future babies. I figure I'll get a new lens or two down the line.