As a user interface developer, I come across those annoying question marks in Firefox fairly frequently, where someone has copied-and-pasted some text from a rich-text editor into an HTML file which contained unencoded HTML character entities. I have a fairly good memory for these things, but inevitably I have to use Google to find some that escape my memory. So I developed a simple HTML application to copy the encoded HTML character entities to my clipboard, ready to be pasted directly into my HTML.
The site is still in Beta, which means there are probably a few bugs loitering here and there. I have tested it in a number of browsers and it seems to work pretty well. I think the large type helps to find the exact charcter you need, and the one-click copy-and-paste saves having to highlight some tiny text (as I would have done previously).