Stephanie, Steve's suggestion that the foundation is settling would normally, and may be, the correct assumption, but you mentioned that these cracked brick do not follow each other, and that doesn't follow the usual pattern you would find with a foundation problem. Usually these cracked bricks would be located close to each other in a near straight line, or in zig-zag fashion if the foundation were moving. Along with this, and something not mentioned that's important here; one other telling item is that not only will the brick be cracked, the mortar joints will also be cracked or displaced, leaving a narrow gap beside individual bricks. Check for this before deciding that your foundation is on the move.
Individual bricks can be replaced, but if they are going to "spot" in new bricks here and there all over the outside of the home, you're likely to not like the end result, as it takes a really good mason to do this and not have it show up. It may look ok up close, but often from a distance these bricks stand out because the mortar color usually slightly varies from the rest. I'd get as much professional input on this as possible before making a decision on what's to be done.