From your suggested use of tar, I presume you're using Unix. That given, bacula is rock-solid. It is somewhat painful to set up, but once you get it configured it does its thing with great reliability. There are a number of features you can use - multiple clients (of course), multiple tape drives, unix/windows clients (and probably MacOS too, though I can't say for sure), encrypted backup tapes, bare-metal restores (and other disaster-recovery features), backups to disc or WORM media (eg, DVD-R). I haven't used all of these features, but I've used a lot of them, and bacula has saved my bacon on a number of occasions - and my users' bacon on many more.
One suggestion I'll pass on from a colleague, with which I'd agree, is that bacula works much better with a tape library than it does with a single tape drive. An old stacker can be had for a song (I use a 6-tape DDS-4 stacker at home, which I picked up for less than £200), and if you're talking about tens of gigabytes and thousands of files, I suggest that such an investment is probably within your grasp.
I also accept that prevailing wisdom is that disc is now so cheap that backup to sequential-storage devices (ie, tape) is an old man's technology. All I can say is that for the price of another box of tapes, I can extend my point-in-time restore capability from four months to eight, and that tapes not in use can be offsited much more easily than an HDD could.