The de facto standard GUI program for burning CDs is X-CD-Roast, which is a great program. However, X-CD-Roast has been around for quite a while, and it can be somewhat difficult for people to use. A relative newcomer to the CD-burning scene is K3b, a KDE-based program that many say is one of the most feature-rich GUI CD-burning programs available.
One of the nicer features of K3b is its setup wizard, which lets you configure the paths to a number of different programs that allow you to execute various operations in K3b. Besides the standard cdrecord and mkisofs recording programs, the wizard also looks for programs such as cdrdao, vcdxbuild, etc. These base programs allow K3b to do such things as create video CDs, audio CDs, and more.
Once you've made your way through the wizard, you can fire up K3b and begin burning CDs. To burn traditional ISO images, go to Tools | Write ISO Image. Under Tools, you can also copy CDs within K3b, erase CD-RWs, encode video, and more.
K3b also supports projects and sessions that allow you to organize files you would like to burn to CD and create multisession CDs. There isn't much you can't do with K3b, and the slick user interface and attention to detail make this CD-burning GUI a keeper.
For more information, check out the K3b Web site.