We are planning to take a hybrid approach and will put siding on our addition but brick the foundation to tie in the old house with the new addition. Our foundation comes up quite a bit in the back because of the slight slope of our yard so it will be clearly visible in the back of the house. We've opted to try to reuse the brick from our garage and back porch (more pictures just uploaded to the "Before Pictures"). Although this is more labor-intensive because the mortar has to be removed from the brick before it can be used, it can ultimately save you money because you do not have to buy new brick and you do not have to dispose of the old brick. Also, depending on how old your brick is, it may be hard to even find new brick that matches, not just because of color but because of older bricks are generally smaller than bricks currently on the market. It's also a much "greener" approach to building which we fully support (we plan to incorporate some other green elements in our renovation).
Our builder took a hunk of brick out of the back of our garage over the weekend (as seen on the picture at the right) so that he can work with his brick-layer to match the mortar and examine the brick. Jim the builder (as opposed to Jim the husband) thinks that the brick can be reused because the mortar seems to come off easy enough and the bricks are hard enough. Fortunately we have a lot of brick to work with from both our garage and our brick back porch (photo above) which has to come off to accommodate our addition.