I use a lot of these myself, such as Notepad++, 7Zip, VirtualBox, etc. A list that everyone, even if there are some utilities you don’t find useful, should take a serious look at.
However, one of the utilities that stands out is the Ultimate Boot CD 4 Windows. This will create a bootable CD that starts the WindowsPE system and has many utilities that can be used to repair and fix problems on an existing Windows system. It also has some command line utilities, such as a password reset utility.
By having a USB drive with an assortment of tools along with this CD, you should have almost all the tools you need to fix or repair a system!