How can I restart my taskbar?

Open the start menu and then Ctrl+Shift+Right-click in any blank space above, around or on the "Shutdown" button will bring up an option to "Exit Explorer" as shown:

I originally found this on HowToGeek and have used it in Vista for the last year. It results in a much more graceful closure of Explorer without actually logging you out.

You will still need to open Task Manager in order to launch Explorer again though, Alex's answer details how you can quickly bring up the task manager to relaunch Explorer.

The same can be done on Windows 8 by doing the same action on the taskbar instead (thanks to Karl in the comments). This is presumably as the Start button is now missing.

A quick and dirty way to restart the taskbar is to simply kill and restart the explorer process.

Ctrl+Shift+Esc go to the processes tab and look for explorer.exe. End the process, and select File > New Task (Run...). Enter explorer.exe into the field (specifically the filename "explorer.exe", you do not need to enter the full path and it may not work properly if you do), accept, and your taskbar will re-appear.

You could also create a batch file to automate it.

1. From the start menu type notepad then press enter.

2. Type the following in the new notepad.

   taskkill /f /im explorer.exe
   start explorer.exe
   

3. Save the file as fixTaskbar.bat and save it on your desktop (or somewhere else easy to access).

When ever it has issues, you can simply double click on this file and it will restart it automatically.