All my ringtones are custom made, by myself or others. Only one has problems playing and that's an error on my part.
Some ideas that might help
1) make sure they are not in a zip folder when adding them to iTunes extract them first (if there zipped)
2) add then to iTunes first before you add them to your iPhone adding directly to your iPhone seems to cause problems
3) make sure they have no other information in the info tab of the ringtone properties, as this will also cause problems.
4) try manually adding them to your iPhone from iTunes (not directly from the folder they are in) as apposed to syncing them over using iTunes.
Try creating a new ringtone and following the above advice to see if the old ringtones somehow got corrupted (a stretch I know but never the less a possibility).
Any ringtone over 40 seconds will usualy not show up in your list of ringtones.
Hope this helps you people with tour ringtone problem