similar ones. Google Drive, Box.net, Amazon Cloud Storage and Microsoft Skydrive. I use Skydrive to back up my photos as I got in early on it and got something like 20 GB free. I think it automatically syncs folders, similar to what you describe with Carbonite. I don't think the others do that automatically. I think right now Skydrive is offering 7 GB for free.
I use Google Drive for pretty much all the documents I want to save and sync. It's nice to be able to edit almost anywhere from a browser.