Xah Lee, 2009-08-25
Arial Unicode MS. Comes with Microsoft Office and Mac OS X 10.5. Not monospace, but contains the most unicode.
Lucida Sans Unicode. Shipped with since Windows 98. This is Arial-like and is the best among my choices for fancy unicode work. I use it most of the time now. However, it's not monospaced, but that turns out pretty for coding. In a given window width, you now have almost double the number of chars. (and i don't care for formatting practices that make comments boxes or alignment like a ASCII Art)
However, variable-width font is not convenient in dired, and unusable for M-x calendar.
Lucida Console. Default TrueType font for Windows Console (cmd.exe). (in fact, the only choice. The other choice is a bitmapped one.) Reasonably good.
Lucida is a big family. It is extended to include serif, sans serif, monospace and variable-space.
Courier New. Default on Emacs for Windows. Classic. Pretty good.
Fixedsys. The default for Notepad in the 1990s. Bitmapped. More unicode chars than Courier New.