There are a lot of ways to get ringtones on an iPhone. Some are easy. Some not so easy. Some are free. Some cost money.
A new release of PocketMac Ringtone Studio is about the easiest way to get ringtones on your phone, but it is not the cheapest. I think many users will be glad to buy the app, though, in exchange for the extreme ease of use.
Essentially, you drag and drop any MP3, AAC, M4A or a Quicktime movie file onto the app, highlight the part of the waveform you want, decide if you want to fade in and/or out, and Ringtone Studio will open iTunes if it isn't already open and put the file in the ringtones bin. That's it.
You can boost or lower the volume of any clip, and you can zoom in or out of the waveform for precise editing. Note: There is no onscreen button letting you know you can zoom. It's in the built in help files. You use Command-+ or Command-minus.
The only other thing I would like to see is the ability to rename your ringtone before sending it to iTunes. You can certainly rename it there, but doing it in the Ringtone Studio app would be perfect.
As I said, there are a lot of ways to do ringtones. You can buy them from the Apple, or use GarageBand, but I find the process has far too many steps. One favorite of mine is the Audiko website, which allows you to upload your clips, edit them online, and then download them and drag them into iTunes. It's free, and does the job.
Version 2 of Ringtone Studio is US$29.95 and has a 90 day money back guarantee. You can see some videos of how it works on the PocketMac website.
I think the app is a bit pricey for what it does, doubling in price since we first reviewed it, but it is very powerful and very easy to use. I think a lot of people will find it a perfect solution. Early buyers can get a free iPhone case. Ringtone Studio works with all iPhones, including phones running iPhone OS 3.0 and the new iPhone 3GS. The software requires Mac OS X 10.5 Leopard or above.