"must read" sci-fi novels and series?

Help! I need suggestions for really good science fiction novels to read/ listen to. I convert books from pdf to mp3 format, and listen while i drive/work/live, and I would appreciate suggestions from people as to what to listen to next. i have read:<br /><br />the honor harrington series<br />the lensman series<br />conrad starguard series<br />foundation series<br />2001 series<br />most of the drizzt du'urden series (i do SOME fantasy)<br />ringworld series<br />poslene series (john ringo)<br />freehold series<br /><br /><br />I also have a collection of programs to easily convert from pdf to mp3 if anyone wants them. i have access to about 14000 titles, so i'll probably have anything you suggest. <br /><br />thanks, <br />copycat042