"Is there any salvage value in a 24" imac? Could it be used as a monitor for another computer? Door stop? Seriously--I'm not sure what to do with it."
An '08 24" iMac is still a very useful machine.
I see two options:
1. Have the internal hard drive replaced (replacements are not expensive). There may be 3rd-party "independent" Apple resellers/repair shops near you that will do this for a very reasonable fee. If you are handy with tools, patient, and do your homework before starting, you might even be able to do it yourself.
2. Get an EXTERNAL hard drive, and use that as your drive/boot source (essentially "ignoring" the defective internal drive). It will take a little longer to boot up, but once up and running, will be pretty much as it was before.
For option 2, I'd suggest one of these:
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias=aps&field-keywords=usb+sata+dock&x=0&y=0
(many items shown, they all work the same, just pick one you like that's cheap, some are only about $20-25)
....and then get a "bare" hard drive from the vendor of your choice (I like newegg.com).
Just install the OS onto the "docked drive" as you would do onto the internal drive. Do the installation, run software update, create your accounts, then just remember to turn the dock on before you boot up.
Once up and running, you might even get the internal drive running again, at least for "scratch storage space".
Again, if it's only the drive, and the rest of the iMac is still functional, it should have a few more years left in it....