We've been tinkering with
MS System Center Data Protection Manager. It's more or less a client for your windows servers that uses Volume Shadow Copy but instead of copying to the local drive, funnels the shadow to a central server, which you can then back up with tape; if you've seen Windows Home server in action, it's using the same technology. So far it's looking really good; we set up a gigabit backchannel network just for this purpose, and are going to buy a cheap (yeah, $14,000 is cheap in this case) 12 TB iSCSI SAN appliance to support it; we then use 4Gbit Fiber to send it to our tape library for off-site storage. It's halved the backup time for our servers already, and it's not even on the final hardware yet.
BTW, if you don't have a plan for going to tape or an off-site disk based mirror in addition to a locally hosted disk-based backup solution, you'd better have your resume ready. You can't send that drive array off site, and a fire or catastropic overheat in your data center would wipe out your backups as well as your live data; you MUST have a plan for getting things off-site, or at least a good distance from your live data. or there's no point to the backups in the first place.
Last, be absolutely certain that you test your recovery plan; it's no good to back up if you can't get the data back.