I've become a big fan of Arq, although your collection may be a bit large. Crash Plan and Backblaze do well too.
If price is an issue, and you don't care about security, I would also consider a private Flickr account for photos and iTunes Match for music, and then use Dropbox/Arq for the documents/other valuables. Photos/music are fairly safe offsite with those, then your docs will be in S3/Glacier with Arq. Not perfect, but an alright solution for cheap.
As I understand it, some of those solutions won't work because they require you to keep a copy on your machine too no? I believe Backblaze and Dropbox does. That won't work if so.
If price is an issue, and you don't care about security, I would also consider a private Flickr account for photos and iTunes Match for music, and then use Dropbox/Arq for the documents/other valuables. Photos/music are fairly safe offsite with those, then your docs will be in S3/Glacier with Arq. Not perfect, but an alright solution for cheap.