Excellent
I have used quite a few converters and this is the one that I nearly always use. It has a very plain, almost boring interface (a benefit, as it is 100% function) but easy to use. It converts multiple different units quickly. There is no messing around with setting what units you want or dont; just enter an amount and start typing your units and they pop up. I got this for free, but would gladly pay $1-2 (Im not sure of the price).
John Taxpayer about
Convert Any Unit