InfraRecorder is a free CD/ DVD burning application with plenty of surprisingly powerful features.
The program supports all the disc burning projects you'd expect, for instance. You can create data and audio discs, and video DVDs, as well as creating ISO images from disc contents, or writing images to disc (ISO, CUE, IMG, BIN and RAW formats are supported).
InfraRecorder is generally simple and straightforward in operation. If you've ever used any other disc burning tool then you're already familiar with the basics: choose a disc type, browse an Explorer-like folder to locate the files you want to burn, then drag and drop them onto a work area.
But if you like to get into the low-level details, then there are plenty of options available for you, too. You're able to create custom mixed-mode projects, for instance; the program has four different methods of erasing rewriteable discs; and when burning regular discs you can choose from six write methods, opt to allow overburning, swap the audio byte order, or enable or disable a variety of manufacturer-specific write modes (depending on your hardware).
This is the portable version of InfraRecorder.