Whenever you build a new computer what are the first things you like to download once the OS is installed? I want to compile a list because weeks after the install I always realize I forgot to download things like VLC player, update Java, Flash player, DirectX, etc. GO!
The most essential thing to download and install after Windows is up and running is the network driver so you can immediately follow that up with downloading and installing online security software, including the latest virus definitions. Nothing is more important than setting up online protection.
Agreed with Phillip, first is drivers and get Windows up-to-date. As for software is depends on user, but the most common are your favorite browser, Flash, Java, Adobe reader, 7zip, Notepad++, VLC (or install full codec and use default WMP), MSOffice if you have, OpenOffice if you don't have MSOffice, Security software (malwarebytes, Avast, MSEssentials).