I keep away from seriffed fonts unless they are very large. I usually add an edge a couple of pixels wide, in black or a dark color, then a separate drop or cast shadow, to make it pop off the background. I make sure the text color is complementary, that is to say, across the color wheel from whatever the background color is. A handy way to check for best color and contrast is to switch your monitor to B&W or monochrome, and if the letter still pops well, then likely people who are color-blind will still be able to read it, and normal eyes will find it very easy and dimensional.
Art and craft stores sell color wheels, These are handy to have nearby. Also you can find free ones online. Many of those are made for web masters as guides to pick harmonious colors for web designs. Or you could use THIS:
http://www.digitaljuice.com/djtv/detail.aspx?sid=578
