An economical alternative to a key tower is the Rack-It system. You supply a sheet of 1/8" or 1/4" pegboard, and use the Rack-It system to create your own key blank display.

Automotive Rack-It System
(Part # 474-00-8X)

Contains 10 automotive key racks (10 hooks per rack), key ID strips with blank boxes for numbering, and one reversible header. This system will organize 100 different automotive key blanks.
 
 
 

Residential Rack-It System
(Part # 475-00-8X)

Contains 13 residential/commercial key racks (12 hooks per rack), key ID strips with blank boxes for numbering and one reversible header.  Will organize 156 different residential/commercial key blanks.