Everyone has software they've learned to depend on. My list has grown alarmingly long, but thought I'd share it here.
Firefox (with Adblock and Flashblock)
Microsoft Security Essentials
Chrome (always need a backup browser)
Arcsoft TotalMedia Theater 3 (blu ray playback)
Slysoft VirtualClone Drive
And the video encoding/authoring/editing tools:
BD Rebuilder (and the auxiliary programs ffdshow and AviSynth)
There are many others I use, like Audacity, foobar, DVDLab Pro VideoReDo, etc., but the list above is the core of what I have and use on my machines. Surprising how many on the list are free. They have proved to be extremely capable nevertheless.
What's important for you?