Dero is one of the main companies that makes bike racks (they also support bike advocacy initiatives):
http://www.dero.com/commercial_racks.html

They have the typical U-shaped and "Staple" racks, the sine-wave style, pretty much anything.

(no connection, I've just used their products and like them)

I'm sure there are cheaper ones out there, too, but beware the real junk that just bolts together - it can be easier for a thief to take the rack apart to steal your bike than break the lock!