I think most, if not all, of her songs have a distinct sound.
I do think all of her interludes and introductions are the most distinct.
A lot of her old words seems very unique, including And Then, monochrome, SURREAL, TO BE, and WHATEVER.
Others I feel are kind of distinct are kiss o' kill, M, Naturally, NEVER EVER, RAINBOW, and still alone, though I feel those may be just because of her, not sound (excluding Naturally and kiss o' kill).
Definites?
alterna
Bold & Delicious
flower garden
Free & Easy
INSPIRE
Ladies Night
Real me
until that Day...
WE WISH
Will