The X-Com game I preordered. Mount & Blade Warband
I can't think of any others. Demos sell games for me at full price, if the demo is omitted, I won't pay full price for the game. The original mount & blade I was late to the party so I bought it cheaper (I bought it immediately after playing the demo), but I paid full for warband. For x-com, the demo sold me on the game immediately and I pre-ordered it.
I don't understand why we stopped with demos. You wouldn't buy a car without test driving it. You might download the car but that's a different issue.
He who stumbles around in darkness with a stick is blind. But he who... sticks out in darkness... is... fluorescent! - Brother Silence