There are times when you may want to set an alarm, but you want to a discrete one--one that notifies only you (and not everyone sitting around you) when it's time for whatever-it-is-you-want-to-do. For example, maybe you're a sleep-deprived (or just plain lazy, who am I kidding) student and you want to take a nap in the library! However, you also don't want to oversleep and miss your next class. How can you do that without interrupting your neighbors? A vibrating alarm! One that's set on your iPhone, nestled under your arm as you nap with peace of mind.
It's true, the iPhone doesn't come with a silent, vibrating alarm feature. Sucks, right? WRONG. After doing some experimenting, I have an easy solution for those interested. It will simply cost you $1.29 and maybe a couple of minutes.
Purchase a Silent Ringtone
 Go get your iPhone (as if you're not tapping away on it already).
 Go to the iTunes store using your phone.
Turn on the vibrate
 Go to the iPhone's 'Settings' feature. Tap on Sounds. Under the Silent section, set Vibrate to 'On." This step is very important. If you forget to do this, you will have an actual silent ringtone. Which means you will basically have nothing. Epic fail. (I know, ringtones that don't vibrate probably don't qualify for 'epic,' but it would be a pretty sad thing.)
Set the Vibrating, Silent Alarm
Now you're ready to set your alarm!
 Tap on Clock. Whether you're using the Alarm feature or the Timer feature, the key step is the same. The sound you want to assign for the alarm will be 'Silent Ringtone' (the one you just purchased from the iTunes store).
 Now you're all set! And you can make as many vibrating ringtones as your heart desires.
It feels good to outsmart the iPhone, right? ;)