Though I've never (yet!) written a successful commercial program, I do a lot of programming, mostly for my own benefit. But whether you're programming for yourself or for a market, these are some tools that have made it a lot easier for me to develop professional-looking programs. Needless to say, every last one of them is FREEWARE. I despise high-priced software. Why? Because it costs so much. Duh!
Don't fool around with interpreted languages. Nobody wants to buy a program where you have to bring up some damn programming environment just to run a particular app. And while I love Just Basic (see below) for quick-and-dirty testing, and I know it produces so-called stand-alone apps, they aren't native .exe files. So forget that.
I recommend Visual Basic 2008. I give an extensive discussion as to why here. In brief, it's free, easy to install, produces native Win apps OR .NET apps OR console apps, and you can do practically anything with it.
Bringing up the Immediate or Debugging mode in VB is a pain, and it's slow. Don't neglect having a good calculator available just to quickly figure out what half the size of a control would be, or to work out constants in some scientific program. Make sure you have an easily available shortcut to the calculator. Note that it has both regular and scientific modes.
Did you write a program three years ago with a color on some control that you want to use again? Want to match some color you saw on the web or in another program? But you have no bloody idea how to reproduce it? Can't find the original code? Can't tell what they used in their web page?
ColorPic lets you move a target pixel around anywhere on the screen. Wherever you go, it lets you know the color of the pixel you're resting on. Decimal and hex code, both of which can be copied. Also Hue, Saturation, Value, and R G B values. And C M Y B. And it includes a little magnified window so you can be sure you're getting the color you want if you're focussing in on some tiny graphical feature. And more. This is just a magnificent little app Iconico developed. Free to download from here.
Doing anything with a web site? Need a quick way to upload and download files to your site? FileZilla is simple to use, let's you drag and drop from a folder on your hard drive to a folder or site on the web and back, gives you pop-up command choices, and in short, is a great little ftp program. Free here.
If you're developing for a market, sooner or later you'll need an icon for your company, to put in the upper left corner of your apps. Or for some other reason. IcoFX is a fairly simple, easy to use icon writer with a bunch of painting tools, zoom in and out, and different size icons, and it gives you a genuine Windows .ico file. Free here.
I love Visual Basic, but their "Click-Once" deployment is for the birds. If you want serious control over the app you're developing, and how it will setup on the user's computer, get this Inno thing. It pretty much does the work for you. You write a script for how everything will go down, using wizards and other things to make it easy, and you run the script. Bingo, it produces a setup.exe for you (yes, you can change the file name). From Jordan Russell's Software. Free here.
If you want to check out an algorithm fast, or need a hyped-up calculator available, Shoptalk Systems has the lovely little freeware interpreter, Just Basic, available for free download here. It can do GUI as well as console, has a fairly extensive set of commands, and runs pretty quickly for an interpreted language. Warning--it has the original, devastatingly stupid "just use a variable in order to declare it" early Fortran/Basic syntax.
Want to copy a graphic you found on the web? Or screen-capture a program? Or pretty much grab any picture of anything off your computer screen? Mirek Wojtowicz wrote a little thing called "MW Snap" (version 3 is the latest) which can do it. You pick "Fixed rectangle", or "Any rect. area" or "Window/menu" or "Full desktop", click the "Snap fixed rectangle" button, and there it is. (For "Any rect. area" you have to bracket the area with the mouse first, then hit Enter.) Save it as a bitmap, JPG, GIF, PNG or TIFF file, at any of a choice of color depths per pixel. I love this thing. Get it free here.
You've written this cool program, debugged it, deployed it. You test it. Uh oh. You missed something. It crashed unexpectedly. You've got bugs. You need to rewrite. And you just set the thing up on your computer.
That's where VS Revo Group's Revo Uninstaller comes in. This is a hell of a lot more powerful than Windows Add/Remove Programs. It finds more things programs leave behind than Windows does, and it gives you options as to which registry values and folders to remove once the app is uninstalled. I usually just delete everything. Available free here.
Th-th-th-th-that's all, folks!