Wow, this was something I was about to write in about, only my girl is not quite five. I'm going to try the music from her and check out Meditainment.com for myself!
My husband is badgering her about quiting and I don't think it's helping. He told her she shouldn't suck her thumb at night anymore on night recently. I think she took him seriously and tried not to, but when I went up to check on her around ten, (she's usually out like a light 20 min after we leave the room) she was still wide awake and anxious and asking which thumb she could suck.
I think Erin T's on to something and I'm going to try her suggestion with Erin (my girl), too. Bad tasting things on their thumbs (and batting gloves!) are all well and good, but it still doesn't take care of the reason they're doing it in the first place.
*sigh* Uphill battle for both of us. Good luck to you and wish me luck, too!
-S. K