Lurking on the archlinux wiki, I found a very interesting resource for choosing a strong, easy to remember passphrase. It's called the diceware method. You basically pick a die and throw it repeatedly to determine the words of your passphrase.
To associate a word with the results of the die, you are given a list of words that looks like what follows:
... 46154 ox 46155 oxyda 46156 oxyde 46161 oxyder 46162 oy 46163 oz 46164 ozone 46165 ozones 46166 p 46211 pa 46212 pacha 46213 pack 46214 packs 46215 pacte ...
The numbers indicate what word you should pick on the base of 5 throws. For example if you throw 4, 6, 1, 5, 5, you should pick the word 46155, which is "oxyda". You then repeat this process until you have 6 or 7 words. Pick the words in the order you got them, and you now have a new secure passphrase.
What I like about this method is that it is fully automated, yet perfectly secure. You don't have to worry about making a choice: the die makes it for you, and you still end up with something that is easy to remember.
Sure, I read xkcd and I was already using long sentences that made sense only if you are me, but this method beats mine, since there is no way I was picking these words randomly.
Since I could not find a list of french words, I quickly made my own.