What are the ALT and CTRL buttons for?

Along with a little help from my brother I've compiled a short list of keyboard shortcuts involving your alt and ctrl buttons.

Alt + Tab = switches between open windows (any open windows)
Ctrl + Tab = switches between tabs in firefox and internet explorer
Ctrl + mouse wheel = zooms in on screen (mostly the text)
Alt + F4 = Closes current window
Ctrl + L = selects/goes to address bar