Is there any way of converting the triangle fan found on a cylinder cap into quads.
If you know that your circle has a even number of vertices, and do not care how the gird is aligned; then select all the vertices in the circle with alt RMB , then ctrl F > grid fill.
Select half of the vertices of the circle. The selection needs to have the same number of vertices along the top and bottom, and the same number unselected on the side.
Then press ctrl F > grid fill.
Which will give you this.
If you intend to subdivide the mesh later (eg. using Subsurf modifier) and use only Grid Fill on the cap, you will get distorted mesh, despite the fact that it's all quads.
In such situations caring about all quad faces is not enough and filling the gap with simple Grid Fill operation won't do the trick. You need at least one additional edge loop on the cap before using Grid Fill, like the mesh on the right shows: