It makes me sad when I find out that a lot of people use bad tools, so here is a list of tools that I use almost everyday (as of May 2013). Most of them are great & some of them are acceptable. Feel free to suggest better tools.
Your life is miserable without these
There are 2 types of people:
People who try to open a movie with Windows Media Player, but find that they cannot open any movie with it, so they download the XviD codec & install it. Later, they try to open a movie with extension RMVB, then they find that they want another codec which conflicts with the 1st codec, so they remove the 1st codec & install the 2nd, but not all movies requiring XviD works, so they ask a friend who tells them about the Combined Community Codec Pack which plays all kind of videos except Real Media & QuickTime, but if you install Real Alternative & QuickTime Lite to play RM & MOV videos. Now they just need to install DirectVobSub for subtitles & they are finished. This is just for Windows.
The 2nd type of people installed VLC player & lived happily ever after.
So you want to search for files by their name or extension. You open Windows search & type the file name, then you wait, and wait, and wait, and ....
During this, I downloaded & installed Everything search engine, searched for the files I need, found them & already working on them.
Now, Windows just showed the results. Please remind me why I searched for these files?
Why install 48 MB slow application to view PDFs when you can install a 5MB lightning-fast application which can view PDF, MOBI & many different formats?
Which one you choose depends on you, but you should not use IE.
Swiss-army knife for raster image editing. What MS Paint is supposed to be.
Free Virtual CD program without ads. You won't find a better one.
Free & easy to use download manager.
Did you see James Shore series Let's Play TDD & wondered how you are going to download all of these videos to see them offline? youtube-dl can download from youtube & tens of other sites as well.
FFmpeg is a media conversion tool. I've mixed feelings against it. It's very powerful & fast, but also very hard to use. Each time I've to google how I can use it, but it's performance makes it practical than other conversion tools I tried.
The best crap cleaner & disk defragmenter.
For command-line gurus
It's a shell container which groups all your shells in a single window with multiple tabs, including putty.
A smarter shell for Windows. I like that when you press TAB it shows all the available options, instead of cycling through all the options. It also supports persistent history.
For the Ninja programmer
I used different programming languages, but Python is the swiss-army knife that I use when I've the choice, and it didn't fail me. I used it for small scripts, GUI apps, to high-performance web apps.
I wanted a powerful text editor (like VI or Emacs) but didn't need me to relearn how to use a text editor. I used Notepad++ for a long time, before I switch to Sublime.
SQLite is convenient for development, because it doesn't require installation of any kind.
I had nice experience with Postgres when I built rawa7.com. Installing PostGIS (Postgres GIS extension) with other GeoDjango dependencies on Windows is painful, but after this it's a joy to use.
It also supports compression, recursive queries, Multiversion concurrency control, custom types, table inheritance, regular expressions & other interesting features. DB choice is probably the hardest thing to change in an enterprise, but Postgres is worth a try.