About a month ago I received an e-mail from the developer of qwikCONVERT, my all-time favorite unit conversion widget. I was afraid Ben had stopped developing this widget, so I am very happy that he did not. Among other things, this update corrects currency update issues and now finally corrects problems when converting negative numbers, a big problem when converting temperatures between Celsius and Fahrenheit.
If you have never tried qwikCONVERT, I urge you to try it. As far as I know, it the quickest and easiest way for unit conversions. Simply enter the amount you want to convert and the units (e.g., 25 C) and you will instantly see conversions into other applicable units (e.g., F and K).