At an Amazon Web Services conference I was at this week, I stopped by the booth of online photo service startup This Life. I'm not at all affiliated with them, but I found their offering interesting.
Specifically, their "Icebox" service is $3/month per 25,000 photos or 100GB. They'll store JPEG and RAW photos. For twice that cost (i.e. $6/month per the same), you get other management features, like automatic face recognition, tagging, and etc.
This service is backed by the Amazon cloud, and uses the new Glacier service behind the scenes, which is how they can offer the relatively low prices.
As with any small startup company doing something like this, there's obviously a risk that they might just go away, so I'd make sure to have a secondary backup as well. Right now, they don't offer any way to easily get your data out, but apparently there is a public API (not yet documented).