My 1930's apartment has one of those "scare you out of your britches" loud mechanical metal-on-metal doorbells. I've been considering replacing it with a wireless model, but I've yet to find one with a tone I like enough to bother. But now I know I can use a $12 9V recording module from the Radio Shack down the street to realize my dream of answering the door to The Smiths "Barbarism Begins at Home" or Guns N' Roses' "Knockin' on Heaven's Door"...
How to Add Custom Ringtones to a Wireless Doorbell by DIYHacksAndHowTos
What You'll Need:Wireless Doorbell (and required batteries) 9V recording module (RadioShack Model: 276-1323) 9 volt battery Wire strippers Wire Cutters Soldering Iron and Solder (optional) Hot glue and hot glue gun (optional)
Seems reasonable enough for anyone comfortable soldering and doing a little rewiring. Of course, you can skip jumping through all the DIY hoops and buy an off-the-shelf MP3 ringtone solution with similar features (which I'd probably do).
Via Instructables, h/t Lifehacker

Shaw's Original Fir...
i like the idea.. but i don't have that many visitors and no one in my complex has doorbells that i am aware of.. plus i would wonder if it could be stolen..
Love this idea.
Stolen? The door bell is inside your house.
omg i disabled the doorbell cause in my teeeeny apt it was incredibly loud ... i would always jump about four feet and my poor cats !
i have had three wireless units but they dont last long. cant wait to try this!
Great idea!
I though Radio Shack was out of business.
We did just the reverse. I hate the sound of wireless door bells and the one we ad was out of tune and out of synch. The first thing we did when we moved was to have the hard wired one restored.
shhh... I don't think he gets out much.
Gregory, I think "How Soon is Now?" would be a better Smiths choice for a doorbell -- especially for a non-social person like me.