I like using the Simple Passcode option on my iPhone, but I've always been kind of bugged by the idea that there are only 10,000 possible passwords under that scheme. Since it's always 4 numbers, lots of people tend to use a month/day combination which makes guessing a fairly easy task for many people. Is your first digit 0 or 1? Do your 3rd and 4th digits add up to no more than 31? Is your combination your birth year? Last 4 of your phone number?
If you would like a longer