Online Photo Backup

So after Superstorm Sandy flooded my basement I needed to get rid of just about everything down there.  I'm luckier than a lot of people in my area, as my home is intact and I didn't lose anything valuable (to me).  But it got me thinking about online photo backup.  Right now I use time machine on my mac regularly, and I also backup photos to a second external drive.  I'd like to arrange offsite photo storage, and would prefer an online service to a physical offsite arrangement.  I've looked at flickr, iCloud, smugmug, google drive etc.

Right now I have under 50 gigs of photos in my iphoto library, but I expect that to grow.  I'm planning to take my negatives from my pre-digital days to be scanned in, and I'm expecting to begin doing some shooting in RAW with my new camera.

Does anyone here use an online service like this specifically for their photos and have advice about which service to go with?