Need Random/unique &&"ID's&&" For Key Verification

I need to be able to create completely random and unique keys for a key verification system, which would require a user to enter a pre-defined key in order to activate their account, but I need to be able to create those keys on the fly.

This is going to be a key that will be mailed to them on paper, and unfortunately means it needs to be relatively short in order to prevent too much confusion while they are typing it in.

I like the newID() function in SQL, but the ID that it creates is a bit excessive to say the least for someone to have to type when registerring.

I use C#, so I wouldn't have much of a problem creating a small app to create x number of keys, which will sit in the DB until I need them, but I would rather not have to fill the DB with a million or so ID's which might never be used, and don't want to create too little that I have to track when I might need to add more, in case I start to run low on ID's.

Re-using ID's may be an option, but I would prefer to keep them intact for the life of the accounts.

If there is something that I can do to simulate the newID() function, but generate unique/random ID's which look more like this: A97-2C5-77D than this: A972C577-DFB0-064E-1189-0154C99310DAAC12 I would be very grateful to know about it.

Thanks!