Win7 came with a great free calculator, including a full programmer's one with hex, dec, oct, bin, and multiple word length calculations. I ported it to run on my other boxes: Vista 64, 32.
Today, I find calculators are only good if you are working in the lab on hardware, brainstorming on paper, cross checking the computer, the spreadsheet script, or without a computer. Once you get the numbers down, you'll end up transferring the data to your PC for further analysis, so you can't do anything elaborate otherwise you'll duplicate your work. So I use it only for approximation. I use the $9 solar power FX260, which I have 3 and just leave it all over my workplace and home. I also use Real Calc on Android quite a bit, when I'm not within arm's reach of the Casios.
For programming, as you need a computer to program, I use the Win7 calculator since whatever you calculate say in hex, can easily be ported and tested in code if its on the PC already.