Any custom software that is large and complex and used on only one computer.
However if you are talking about off the shelf software I've just ordered 5 copied of Wise Package Studio Suite at just over £5,000 a copy for work.
well for "custom" software i think it would be the software that microsoft made in conjunction with vairous police departments to aide in the caputre of pedophiles i think the liscnce is around 4 mill US.
but for commercial software i think Maya is up there around $11 000 i think.
Softimage Face robot is $94,995, its a high end facial animation software.
But you can get softimage XSI foundation for $495 thats really cheap for a leading 3D animation package it might have a few features taken out but you still get Mental ray rendering.
But this thread is a bit pointless I dont have $495 yet for XSI let alone $94,995
It's hard to define end user. Any scientific software fall in the very expensive also (Matlab, CFD software etc). Also CAD design (ProE, Catia ...) softwares are quite expensive. I have no numbers because i never had to budget any of them myself.
The most expensive I heard was a license for VxWorks which ran around 200 000$.