Best way to cap/enclose open shape?
 

Let's say I make a simple cylinder with no caps (or any similar shape like a cube with no "lid"). What is the best way to cap it off after the fact? Is there a simple, semi-automated way? And by "cap it off", I mean a tight form fitting cap with no gaps and full surface attachment.

Thanks!

Polys: Use Polygons > Append to Polygon Tool

Nurbs without deformation: Surfaces > Planar