I have one of those generic Korean 27” LCD monitors. It’s nice, but Mac OS doesn’t recognize it enough to enable subpixel font rendering. Here’s how to fix it on OS X 10.6.8, via MaxOSXHints:

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defaults -currentHost write -globalDomain AppleFontSmoothing -int 2

Especially with a nice font like Source Code Pro, it makes a perceptible difference in clarity.

Related: A longer web page about font rendering than you probably want to read.