Script/Tool to Auto Hide/Unhide Windows Taskbar

Try using Aviassin Taskbar Eliminator.

I heard it is a good one.

You could use the following AutoIT script for showing/hiding the taskbar (or compile it to executable(s) with so you can run this without needing AutoIt)

This example script hides the taskbar, sleeps 3 seconds and shows the taskbar:

Opt('WINTITLEMATCHMODE', 4)
ControlHide('classname=Shell_TrayWnd', '', '')
Sleep(3000)
ControlShow('classname=Shell_TrayWnd', '', '')

The script has been taken from: http://www.autoitscript.com/forum/topic/27505-hide-taskbar/

This answer uses AutoHotkey:

How to toggle the auto-hide status of the Windows taskbar

You can set it to whatever key combination you need.