I want to know the name of the American film production company that
currently holds the film rights to Iain Banks' "The Wasp Factory."

Many sites on the internet referrence Iain Banks being in litigation
with an American company in an attempt to reclaim the film rights to
his novel - I've included a link with this information.

http://www.futurehi.net/phlebas/text/archnews.html

This might be of some interest to you (scroll down to page 9, "The
Story of the Film"):

http://banksoniain.netfirms.com/banksoniain_01a.pdf