I cannot say with regards to chapels and oratories, but all churches, ie parish churches, cathedrals, etc should have a baptismal font. The church would be incomplete without one. I do not recall ever seeing a church without a baptismal font, although I do know many which have portable ones (which I do not like at all, but that is my opinion). I love old traditional churches which had the baptismal font at the side, in a nave, even behind a gate, as SMHW describes.
The modern idea is to put the font at the entrance to the church, inline with the altar and tabernacle (assuming it is in the church), the idea is it an architectural sign that baptism brings you into the church and towards the other sacraments. The idea is not without merits, but I believe it is less than ideal from a practical standpoint of liturgy. Other new churches are being built with them in the front, to the side of the altar. I actually like this. It works particularly wellfor Easter Vigil mass.