What to do with a spare 220 line?
It depends.  If it's a 4-wire connection (hot-hot-neutral-ground) you are good to go.  

If is a 3-wire connection (hot-hot-neutral and no equipment safety ground), you have two choices (or not): 


If the neutral wire is a bare wire, you can permanently recharacterize it as a ground wire, and use the two "hots" to drive a 240V-only load (but not a 120/240 load like a dryer).  You move the ground wire from the neutral bar to the ground bar. (in a main panel they may be the same bar).  This option is not available if the neutral is white or gray. 
You can convert it to a 4-wire connection by retrofitting a ground wire.  Fortunately the ground wire need only be #10 and can follow any viable route back to the panel, any other #10 ground or conduit, or the grounding electrode system. 


With that matter taken care of, you can redirect/retask it to another purpose so long as all splices are made in junction boxes which are accessible. 

If it is already a 4-wire connection, or if you are making it a 4-wire connection, leave things in a state where you can convert it back to service for an electric range.  Some jurisdictions require you provision this service, and easy convertibility meets the requirement.