The benchmark in personality is "the big 5". Nerds everywhere will be happy to know that this framework is from lexical analysis - e.g. data mining. The essential features are thus: empirical ("from the field") and reflective of our current society (allowing a comparative study of you versus others). The weaknesses follow from these essential features: no conceptual underpinnings, based on "averages" (persistent and consistent patterns in self reporting and writing), based on self view (if you ever spoke to a jerk, you know they would rate themselves rosy while everyone else would not - so this weakness can be huge) - so if you have higher or more realistic standards and self view than others, you will rate lower in various measures.
The lowdown of the big 5 is this: data analysis reveals clusters of traits that indicate 5 "basis vectors" which build up personality space. e.g. take all the adjectives we can use to describe ourselves, and we can project them into 5 different dimensions that capture how people tend to describe themselves. Simply by taking a test you can see how your personality is described in this 5-d space, which is bound in size in practice by the simple fact that we are finite creatures sharply bounded by time, capacity, and our social environment.
We float on an OCEAN [openness, conscientiousness, extraversion, agreeableness, and neuroticism] with others, and can quickly see how we "measure up" against others. As a simple rule, it seems like we would do well to "max out" on these measures in order to be a successful and happy person (for neuroticism, you want to max out on the low end...).
In short, the big 5 is a fairly flawed system - but one that is quick to determine for oneself, and will give you an impression of both our society and how you are positioned in the personality space of our times. Using your score you can see how others will tend percieve you, how you stand in relations with other, and thus what you may want to focus on in improvement (as we are social creatures our success often depends on the help, or at least not hinderance, of others). As far as personality tests go, this is a decent one and one that is the benchmark. Each dimension gives you a particular area of focus for self improvement, and an actual way of measuring - yes, far from perfect, but a somewhat objective measuring stick to see your progress, weak points, strengths, etc.
