I thought it was because I was using a cheap VGA cable to connect to my LCD monitor, but as it turns out, the fonts looked terrible because I had rotated my monitor into portrait mode.
From ZDNet, Why ClearType doesn’t work in Portrait mode:
I made an interesting observation over the weekend that almost had me thinking I was seeing things. As it turns out I wasn’t seeing things and font rendering technology like Windows ClearType won’t work in “Portrait” (Vertical) display mode on LCD panels. That means if you have an LCD that supports Landscape to Portrait rotation; the text is utterly unreadable if something like ClearType is enabled. This also means that people who have “Slate” Tablet PCs that are held vertically simply will also have a hard time rendering text because ClearType becomes CrapType in vertical display mode.