What Do You Use To Calculate Power/Voltage Drop?

What tools do you designers use to figure factors like voltage drop and power distribution during designs?

I have never used a calculator or a software tool for this. I always did it manually, and I wasn't especially consistent in calculating values. I just over-engineered (wasted money?) a lot following the precept "When in doubt, make it stout."

There has to be a better, easier method out there.

What tools do you use? Any nifty apps or websites to share?

Altronix has some useful calculators on their website.

I just used this one (PowerStream Wire Size) to verify Robert Baxter's calculations, which it did, so I know its accurate... It's layout is a little clunky, though.