I know that I am not the only one whose loses my phone (sometimes with the help of little fingers) because just last week Debra (founder of this here blog, housewife extraordinaire, and my best friend) IMed me to ask if I could call her phone so she could locate it. :)
Next time your phone goes AWOL, try one of these phone-finding apps. They'll place a call to your cell phone so you can follow the ringtone and find your phone.
The site requires no account and no other information, and your number isn't stored anywhere. If someone misuses the service to call your phone, you can place your phone number on the Stop Calling! list to stop all calls from Where's My Cell Phone. And if you know who the offending party is, you can use the sister site PrankDialer to extract your (harmless) revenge.
Phone My Phone is a paying service, but they offer a free trial version. You just enter your phone number, select how many times to call and when, and then click the "I accept. Call me." button to accept the terms of service and be on your way to finding your phone. Phone My Phone also gives you the number that the call will be coming from, so you don't accidentally answer the wrong call. :)
Phone My Phone is meant to be more than just a phone finder: you can use the service's call as a wake-up call, a reminder, or an excuse to get out of a boring meeting. Because of this, Phone My Phone offers a few more options than Where's My Cell Phone: you can call multiple times (up to 5) and set the time of the call for anytime in the foreseeable future. I haven't found a limit yet to the free trial, but I presume that eventually you will run out of free calls so that you are more inclined to pay for the service.
iTag app to see your phone's location and perform some basic functions, such as making it ring, locking the keys, backing up your data, and deleting information on the phone.
If you have a smarter-than-mine phone running an operating system other than Android, check out this article to see if there's an app that will help you find and/or secure your phone.