iOS 5 allows users to set custom ringtones (either those purchased through iTunes or converted to .m4r) for a more comprehensive set of events than before, including new email receipt and email sending.
However, while the built-in alert tones (those that last a few seconds and are suited to single alerts rather than phonecalls) are listed separately from phone ringtones, custom ringtones are listed together. This can make finding alert tones difficult if you have more than a few custom ringtones.
The obvious solution is to use iTunes to add something to the front of the names of alert tones so that they are listed together. The text 'Alert: ' would be functional, but unattractive.
One visually appealing way to list alert tones together is to use Emoji at the start of the tone name. You may browse these in the Edit » Special Characters… menu in most applications, including iTunes for editing these names.
For alert tones, the bell followed by a space works well and moves all such tones to the top of the list. If you prefer to list ringtones first, use an icon such as a speaker, music note, or iPhone at the front of the ringtone names.
[crarko adds: I haven't tested this one.]
Mac OS X Hints