Had a problem comming up with strong passwords for a long time -- it was nearly impossible for me to think of a password that conformed to the requirements of whatever system I was using ('must contain a number', 'must be mixed case', etc). The best way, in a pinch, I found is to use serial numbers and product codes.
They're usually very random, many are mixed case and have good lot of numericals in them. for example, I have a box of candies next to me, and the weight measurment is "NET WT 2OZ 60g", and my changing that a bit you get "WT2OZ60g", which is a mighty fine and mighty strong password. Just make sure you don't copy them verbatim -- change a character or two, just to be on the safe side.