Tape has always worked well for me and has saved me many a time. The company where I work isn't going to let me buy anything else relating to backup for another 3 years because of depreciation.

I think hard disk backup has great potential to replace tape, but I'm still concerned about reliability, especially if the disk has been sent off-site.

Online backups to a remote location with a trusted host would be what I would choose. A service. I would still use my tape backup in conjunction with it. Double backup. You can never have too many backups.