Windows narrator(windows only)

http://www.microsoft.com/enable/training/windowsxp/usingnarrator.aspx

Free

Non Visual Desktop Access (NVDA)

http://www.nvda-project.org/

Free

System Access To Go

http://www.satogo.com/

Free

Hal

http://www.yourdolphin.co.uk/productdetail.asp?id=5

Commercial

JAWS

http://www.freedomscientific.com

Commercial

Supernova

http://www.yourdolphin.co.uk/productdetail.asp?id=1

Commercial

Window-Eyes

http://www.gwmicro.com/Window-Eyes/

Commercial