Khoi’s dilemma with finding an online backup solution for his 400GB of data. There’s some good discussion in the comments with many recommendations for DropBox, Backblaze, or Jungle Disk.
My approach for backing up is to keep it simple, and keep it safe. At my home I’ve got a TimeCapsule/TimeMachine backup, and run a nightly SuperDuper clone to an external. At my work office I’ve got another external that I clone weekly.
Having an off-site or online backup is important because, as Khoi says: “Fire or theft would leave me as helpless as any less-conscientious computer user, rendering all my self-congratulatory local backups worthless.”