1) Get the "standard" 20% corporate/education discount that most phone companies offer
2) Get a family plan which can be much cheaper
3) Get data for cheap (t-mobile offers 200mb data for $10/month)
4) Get free nighttime and weekend minutes
5) Get free calling within the phone network
Most people on prepaid could get a better deal without prepaid if they shopped around a bit.
I would love it if people stopped the misconception that "prepaid is cheaper" and instead realized that different plans are better for different phone usage habits.
Update: formatting, changed one instance of the word "on contract" to "without prepaid"