Firefox is my main browser, as it has been since 2006 or so. While they've made some recent changes I haven't been happy with, it's still by far the best Web browser. I will NEVER use Chrome.
I love foobar2000, it's lightweight (as I like all my software to be), and it supports a ton of plugins for playing various video game music formats. Really fantastic software.
Microsoft Paint (Vista ver.)
Believe it or not, I still use MS Paint for all my pixel art editing. There are some great editors out there, but they just don't really work for me, so I continue to use this. I don't do a ton of pixel art, though, so it's not a big deal that it's somewhat lacking.
The Win7 version messed everything up, so I use the Vista version instead. It wasn't even the ribbon UI or anything, the precision is totally screwed up in it. Selections and stuff don't work correctly.
I use Notepad++ for all text-editing operations, including the markup and programming for this site. It's simple, lightweight, and unlike Sublime Text it's free and open-source.
PaintTool SAI is my drawing application of choice. I've tried most of the others (Photoshop, Clip Studio Paint, Krita) but nothing seems to beat SAI in its simplicity and focus on drawing. I find most other programs to be unwieldy and cumbersome, and generally difficult to work with. SAI is simple but powerful. Customizing brushes in most programs is a tedious pain, but SAI makes it easy. It's also incredibly fast and snappy.
It costs around $50 (one-time payment), and given it appears to be developed by only one dude, you absolutely should buy it if you intend to use it.
SumatraPDF is a lightweight PDF viewer. It's also free and open source. It's crazy how much faster PDFs open with this than they do with other viewers. Highly recommend.