First of all, I wouldn't trust CD-Rs or -RWs when carrying them with you on your trip. CD-Rs and -RWs are very vulnerable to both very high and very low temperatures, therefore, your burned CDs might turn out to be worthless once you've arrived back home.
I would also never trust a harddrive device as only source for backing up my files. The reason is quite simple: Harddrives tend to fail at the worst possible moment, mostly due to vibrations. I've had two harddrives fail me already on a trip therefore I don't trust them anymore. That includes MP3 players like the iPod as well.
The only reliable medium for backups I found was flash memory, either a flash MP3-Player (like the iPod Mini with 4 gig flash memory) or USB sticks (you can get a 1 gig USB-stick dirt cheap these days, I even saw an ad for a 6GB USB-stick for less than 100 bucks couple of days ago) or a lot of flash memory cards (CF of course). If you also bring a tiny USB card reader along you should have no trouble whatsoever accessing your photos whatever device they're saved on. Of course burning your pics on CD-Rs and snail mailing them back home is a backup possibility which can and should be combined with other backup techniques
"Life is not a journey to the grave with the intention of arriving safely in one pretty and well preserved piece, but to skid across the line broadside, thoroughly used up, worn out, leaking oil, shouting GERONIMO!"