Fuller make a nice looking Imperial countersink and bung set which many forumites seem to use:
I am looking for something similar but in Metric, as I need to work with 10mm and 12mm countersink holes and matching bungs.
Has anyone had experience with the following Metric countersink and plug cutters? They seem to be available in 8, 10 and 12mm. I would use them in conjunction with twist drill bits (for piloting the holes).
More details here http://www.fine-tools.com/G312630.htm