Amongst many non-exciting but important things that need to be done in life is "improving your vocabulary." No matter how much you run away from it, you can't deny its importance. Follow some of the software that I have been using:
SAT GRE Crash Course: A shareware version can be downloaded from here. You can run it 30 times before it gets expired. The application organizes Word Lists according to the level of difficulty. After a round of study, you get a chance to test yourself in many ways (fill-in the blanks; multiple-choice questions, etc.). Also, you can maintain a list of "difficult" words for reviewing purpose...a must have, in short.
WordWeb: This is a general purpose English Dictionary. To get meanings (plus synonyms, antonym, etc.) just select a word on your screen and press the hot-key. The best part is that it has a very small footprint (if we can use the word for such small apps) and it's freeware.
The above should be sufficient but in case you are looking for more, get hold of "Vocabulary Wizard 6.3" by Prosigner (search on Download.com if you can't find the latest version anywhere else). This one is Adware but a very organized way of learning that gives you score to each word that you have studied, depending on how many times you got it wrong (or right).
Keymaker: But like all systems it has a weakness. The system is based on the rules of a building. One system built on another.
Keymaker: If one fails, so must the other.
(The Matrix: Reloaded)