I’ve been using Typetester for some time as an online alternative to fiddling around with CSS in order to test out font settings. However, more recently I’ve come across a couple of alternatives that show promise.
The first is Designer Plaything, which, while a little rough around the edges, provides a useful alternative to Typetester in that you can try out different headline / body copy combinations.
With some more font options and some further development — more customization options, user-defined text, the addition of sub-headings — this could turn into quite a useful tool.
Designer Plaything also provides a brightness and contrast check of your color settings, which is a nice touch.
The second is Font Tester. It’s very customizable and, like Typetester, allows you to compare fonts against each other.
However, it doesn’t include the option to compare headings alongside body copy.
It also seems a little bug-prone which precludes me from recommending it wholeheartedly. For example, in Firefox changing the number of columns via the ‘View’ option causes the example text to disappear.