Windows: BurnAware Free has one of the most simple interfaces you can find for making a CD or DVD from a computer. A free beta of its upcoming third release converts many formats to usable discs and won't tax your system's resources.
BurnAware went through some changes a while back, moving from freeware to a paid product, then back to free, but with a default-to-yes toolbar thrown into the installation. The beta of its free edition no longer requires you to un-check a box for an Ask.com installation, which is good, good news. As for the app itself, its filled out its support of many audio and video codecs for creating play-able DVDs, and claims only "1-3% of CPU usage while burning". CD copying, which previously had to be done manually by swapping ISO images, is now an automated thing.
BurnAware Free 3 is a free beta download for Windows systems only.