Evan Anderson mentioned in another solution you could buy a LTO-4 (autoloader, 1 tape / day) - $4,566.00 (the discussion included total cost of tapes for a specific rotation.)
but I don't know specifics on what he or you would recommend for the actual drive and if necessary controller. Show me a newegg URL or CDW, Dell, or HP, or whatever your favorite vendor would be for your solution if you don't mind looking it up or just give me a brand and a model number and I'll be glad to do the leg work myself.
I currently have on have on hand an external LTO 3 drive that uses LVD SCSI interface (and thus have a controller card that has an external LVD SCSI connector). If that card isn't sufficient to interface to a LTO 4 drive let me know.
http://www.fujifilmusa.com/shared/bin/LTO_Overview.pdf shows minimum tape speeds for LTO4 and other LTO formats. It looks like the IBM LTO4 actually has a lower minimum speed than the IBM LTO3. Either way my average server is too slow to feed LTO3/4 without shoeshining so I'm looking for a drive with a low minimum write speed. If you trust the PDF from 2008 that makes my choices
IBM LTO 4 full height
IBM LTO 4 half height
HP LTO 4 half height
but presumably there are other options out there that weren't mentioned in the fuji PDF.
Again I'm looking for a specific recommendation on a drive to buy (and the controller if needed).