Maybe not the most creative thing I've done, but it cost zilch and protected us until I implemented Exchange 2007.
At my old company, in perhaps 2002, our HR person's hard drive crashed with her Outlook PST files on it. And in those PSTs was vital and mostly irreplacable information on our myriad employee benefits. We sent it to Drive Savers, but they couldn't recover the data.
We needed a way to get PST files off individual workstations and given some recoverability. We didn't have disk space nor backup capacity to store the 50 employees' PST files on the network as configured, nor had we the budget for anything that would significantly mitigate the problem. So I started brainstorming.
We happened to have a pair of old Adaptec SCSI cards and a bunch (like 12 or something) of 8 GB SCSI drives out of an old AS/400 lying around, so I thought I'd try to make those work for some kind of solution. I took a pair of identical old mid-tower PCs, installed a SCSI card and four SCSI drives into each, as well as two old computer fans per PC to keep those scorching hot SCSI disks cool. Mind you, there were only two 3.5" bays in these boxes, one occupied by the system disk and one by a floppy drive. So I ripped out the CD drives and all the filler plates, and screwed the drives in to one side of the cage. The big opening combined with the fans provided decent cooling. The PCs had W2K on them, and I configured each for software-based RAID5 for redundancy.
Both PCs were tossed into a server rack in the nice cool Halon-protected server room, plugged into the network, and I wrote a script to use a third-party xcopy utility (xxcopy, I think) to duplicate the PST files from one of the PCs to the other every night. I then pointed every desktop user's Outlook to individually shared (for privacy and security) folders on on of the PCs, and moved their PSTs.
This system ran flawlessly, and non-stop, until September 2007 (or was it September 2006?) when I rolled out Exchange 2007, on a capacious server and with adequate backup capacity.
Total hardware cost: $0
My time: Maybe 40 hours. Certainly no more... probably less.