It's not often you think about what knife to use for the job, if its there its going to be used in a pinch. Although there are certainly knives that do a far better job than others for specific tasks these include the following,
Wide blade serrated sandwich knife - This one only came to my attention when sharpening for cafes. The are not expensive at all to buy but when it comes to tasks like buttering or adding any spread to sandwiches these are king of the crop.
Hawkbill knife - When it comes to needing a blade to cut rope all day or peel stuff these things are awesome giving a lot more control on the cutting and less prone to slipping.
Rescue knife - These are usually tipless or rounded tip knives with glass breakers and seatbelt cutters. the rounded or missing tip allows you to cut close to a person say clothing etc without running the risk of injuring them severely. Everyone should carry a nice sharp rescue knife in their vehicle.