I have used recordmydesktop. I used xvidcap before. Recordmydesktop is command-line utility. But if you are into KDE, you can use frontend krecordmydekstop or gtk-recordmydesktop for gtk frontend.
Use of recordmydesktop is really simple. You just type 'recordmydesktop -o file.ogg'. It records video(in fact, encoding only to Ogg Theora is possible) and audio (but it's necessary to set "record" on master). Yeah, i like it.
EDIT: Just a note. Xvidcap sometimes crashed up, probably due to my slow cpu. But recordmydekstop works fine (that's why i like it