Quicksilver is, well, it's an app launcher .. but it's also a customizable "thing doer." For launching apps, one keystroke (I use command-option-F1) and then I type enough of the name of an app to be distinct, and then hit return and the app launches.
Keystroke, m, a, i, l, return. Keystroke, f, i, r, e, return. Keystroke, t, e, r, m, return.
Did I mention that it learns? The first letter is usually all I need.