What features would be good to see in a Help Desk or what are the major features that a help desk should have?

I'm involved in a non-Simple Machines project in building a Help Desk solution and would like to know what stuff people would like to see, that maybe doesn't currently work/or is used in other software, and just what features in general sell a helpdesk to someone?

Well it's a long list, May be you can check out some existing helpdesk software's like -

Kayako (http://Kayako.com), Vision Helpdesk (http://thevisionworld.com), Zendesk (http://zendesk.com), Cerberus (http://cerb4.com)

Those are some good software's with several features.

Ah you slightly misunderstand, I'm asking what features could be improved, or are desired that are currently missing from most software?

And even features people like in general.