monospace

Suggestions for good monospace font?

I'm not a designer myself, but I am a fan of nice fonts. It's been quite interesting to see how much interesting is being paid to typefaces these days.

By profession, I'm a programmer, so I need to use monospace fonts for nearly everything. While I've heard people gushing on about Helvetica, I've never seen much discussion of fonts that could replace Lucida and Courier.

Can any of you point me to some excellent, readable, beautiful typefaces that follow the monospace standard?