I've just switched to a monospace font called Droid Sans Mono, a free,
Apache-licensed (see below) face. I do all my work — novel writing, blogging, article- and short-story writing, email composition — in a text editor (currently using Gedit, a free and open editor) using a monospace face. Droid shows up very nicely indeed, at a large variety of sizes. I've been using it all morning and I've already switched my monospace preferences to it system-wide.
(via Joshua's Delicious)
Update: From the comments, Javier fact-checks my ass: "Sadly, it looks that Droid Sans is not Free after all, and anyone wanting to use a free-as-in-speech font of these characteristics has to pick between DejaVu (Bitstream Vera license, has italics, bold and almost every character under the Unicode sun) and Inconsolata (definitive version will be under SIL's Open Font License, prints pretty but is not so screen-pretty at small sizes, so far has no cursive or bold)."