I'm partial to using a very broad dictionary: http://app.aspell.net/create?max_size=35&spelling=US&max_var....

It has 50,105 words. Gets you an extra 2.3 bits per word.

Better yet, use the EFF's Diceware list. It's easy to pick randomly from the list (just roll some dice) and the resulting passphrase won't have some of the issues a dictonary chosen one would have, like compound words causing entropy reductions. (EG if fire, truck, and firetruck are included in the dictionary as 3 separate words and you happen to get fire and truck in sequence as part of your passphrase the entropy of those two words is equivalent to the entropy of a single word! Not good.)

> if fire, truck, and firetruck are included in the dictionary as 3 separate words and you happen to get fire and truck in sequence as part of your passphrase the entropy of those two words is equivalent to the entropy of a single word

Not exactly true if they are separate words. In a word-based password scheme, you are treating entire words, not characters, as units. The chance of fire, truck, and firetruck appearing in one password in that sequence, given a 10K word dictionary, is 1/(10K^3). The miniscule possibility of this speaks to the fact that there actually is a large entropy.

I realised after choosing random words that gets annoyingly long to type. In that regard, random characters are better.