be forwarned, however, that the caps option and the planar surface tool, both use trimmed surfaces... these are not very good for attaching or animating in most situations. The best way, imho, is the use of the hulls to create the cap.
This is done, by inserting an isoparm right near the lip of the cyl, scaling in the last hull until it is practically invisible, and then adjusting the hulls to get the sharpness in the corner. Depending on how sharp you want it, you may need to insert more isoparms to sharpen the corner out.
If you don't plan on attaching or animating the trimmed surface too much, though, you can use that.
I have an image demonstrating this in this thread: http://www.simplymaya.co.uk/forums/s...p?threadid=817