My taskbar on Windows 7 happens to disappear from time to time, right after the screensaver comes off. I searched for the problem here, and found some advice that didn't work out for me. I tried something else which did work, however, and thought I should post it here.
My solution was, I entered Task Manager, and ended the process 'explorer.exe'. This made everything disappear of course. Still within Task Manager, I chose File > New Task (Run...) and entered 'explorer.exe'. Simply terminated and ran it again. Everything I had, including open programs and windows, was back, including the Taskbar.