er... I kinda divide them according to what style and what tone I want to observe/learn from most of the time... Just for reference before trying to integrate it with my voice

I try not to focus on only one or two singers of a similar style, cos I don't want to end up completely mimicking them (which I tend to, given the regularity).. and cos since there's too many influences at one go, it'll be easier to form my own voice (cos no choice already haha)
Here's my list~ and I know there are more worthier names to note but these are just my personal preferences in terms of tone/timbre/vocal style etc...
They're not necessary my favourites either (like how I'm kinda obsessed about sarah brightman, but can't learn from her voice) but are chosen with its strongest sense of learning influence I can absorb most easily..
k ready set go!
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Soul and improvs: Early Mariah Carey, Roisin Murphy, Aretha Franklin
Blues and blues feel: Janis Joplin, Tracy Chapman
Folk: Damien Rice, Elliot Smith, Ellis Paul
Rock alternative: Holly Mcnarland, Tracy Bonham
Rock, sharp: Linda Sundbald, Melissa Auf Der Maur
Rock, dark/warm: Nina Hagen, Tina Turner
Rock feel and tone: Sandra Nasic, Bon Jovi, Bryan Adams, Richard Marx , Masha, Tanja Lainio
Classical vocal expressions, powerhouse & tone: Maria Calllas, Cecilia Bartoli
Classical low range: Andreas Scholl
Classical powerhouse support: Floor Jansen
Classical dramatic, high: Inva Mulla Tchako, Leontyne Price
Classical light, high: Kiri Te Kanawa
Classical dark/warm: Tarja Turunen
(long list only because I'm kinda self-learning classical at the moment :S)
Acoustic, light: Ani Difranco, Bic Runga, Emiliana Torrini, Julie Doiron, Kate Bush, Lisa Germano, Leigh Nash, Stina Nordenstam
Acoustic, warm/dark: Suzanne Vega, Sarah Mclachlan, Jewel, Jorane, Emily Haines, Heather Nova, Sinead O'Conner, Andrea Corr, Tori Amos
Acoustic, rusky: Natalie Merchant, Chantal Kreviazuk, Elizabeth Fraser, Cyndi Lauper, Kristy Thirsk, Imogen Heap
Jazz, smooth: Holly Cole, Nina Simone, Nouvelle Vague, Roisin Murphy, Susanna Hoffs
Jazz, warm/darker: Alison Moyet, Cassandra Wilson, Nina Simone
Powerhouse vocal: Shirley Bassey, Dulce Pontes, Anneke Giersbergen
Jaw / facial exercises: Alanis Morissette, Aerosmith, Shirley Bassey
Harmony & choral: Enya, Anuna, Clannad
Range, sharp: Early Mariah Carey, Aisyah
Range, low: Diamanda Galas, Dolores O'Riordon, Amanda Palmer