Apple has built cd burning into the OS lately. It's not the most full-featured, but it's free. There are two ways I know of to use it:
1. Stick in a cdr or rw and it will detect and mount it. Drag files to the CD, eject and it asks if you want to burn it to the CD. Kinda like the built-in packet writing on WinXP, but I think it can finalize the disk.
2. Use Apple's DiskCopy program. Use it to create images of the CDs you want, then use it to burn the images to cdr.
Even though these can work, Toast is probably one of the best/easist burning programs.