Selling your CD collection would be insane. Storing them in the attic/garage would be only a little less so. Some times I listen to something on my iPod that I haven't listened to before and I realize I need to re-rip the CD. Besides, you would need multiple redundant backups to be completely safe.
I'd rather have the CDs. I can take somewhere if need be, play them in my car (don't have it hooked up for iPod yet, but usually copy the CD first), or do several other things.
As I mainly listen to classical music, rather than a list of "songs", I have little need of an iPod. Most symphonies and operas are rather long, so shuffling lists of songs does not interest me much. I could use one on a plane flight, I suppose, but otherwise, I'm fine with CDs.