My advice on your question is to talk it over with your wife as to what she would be comfortable having in the house with her, then research the breeds. There are several breeds out there that meet your criteria.
My family has always owned large breed dogs. Currently we have 2 Pitbull/Greman Shepherd mix. I originally wanted a full Pitbull, but was able to rescue the 2 girls so went with them instead. They have been a great addition to the household. I wanted Pitbull because I am not home all the time and that would have left my mother home alone (Yes I currently live with my mother). Pit's are very gentle dogs and would have been great around my 8yr old nephew when he comes around. My two, the mixes, are very easy going with him when they play.
I remember visiting my Aunt and Uncle as a kid and they had a collie. They let me take him for a walk around the block. Some neighborhood teenagers decided that they were going to try and take my jacket from me. Sundown, the Collie, must have sensed that I was scared when they started coming towards me. He barked, growled, showed his teeth, all the good stuff and the 3 teenagers quickly changed their minds. Sundown wouldn't let me move til they were out of sight and then the only direction he would go was towards home.
Sorry, I tend to get a little long winded, had to stop myself from telling another story. If your wife is the high energy type (likes to run/jog, etc.) one of the more energetic working breeds would prolly do well for her. Bah, starting to ramble again. Just try to match the dog breed with her personality type. Hope this helps.