Convert CUE/BIN images to ISO

Use bchunk (Homepage: http://he.fi/bchunk; Debian, Ubuntu, etc already have it as a package).

bchunk image.bin image.cue image.iso
Convert NRG (Nero) images to ISO

Use nrg2iso (Homepage: http://gregory.kokanosky.free.fr/v4/linux/nrg2iso.en.html; already included in Debian and Ubuntu)

nrg2iso image.nrg image.iso
Convert MDF/MDS images to ISO

Use iat (Homepage: http://iat.berlios.de; already included in Debian and Ubuntu)

iat --iso --input=image.mdf --output=image.iso
Generate an ISO file with the contents of a directory
genisoimage -o cd.iso -r -J -hfs <dir>

The above command creates an ISO image named cd.iso with Rock Ridge, Joliet and HFS extensions.

Mount an ISO image file

Execute as root:

mount -o loop,unhide <iso_image> <mount_point>