Every idiot on last.fm has got a blog like this, so I decided to be an idiot too! :)
The most important thing is that you know that this lists consist to 95% of my opinion and my feelings. I do NOT rate talent in any way.

Female vocalists:

1. Dolores O'Riordan (The Cranberries)
Propably the most beautiful voice I have ever listened to. Very nice colour and tune.
2. Ann Wilson (Heart)
Nowadays she's not that pretty anymore but her voice became even more asskicking.
3. Andrea Corr (The Corrs)
Lovely, smooth voice. Makes me feel very comfortable.
4. Simone Simons (Epica)
Her voice is nearly as beautiful as the rest of her )
5. Floor Jansen (After Forever)
Great variety.

I also like to mention the two Nightwish' vocalists Tarja Turunen and Anette Olzon.
I do not listen to much female fronted music anyway, so this list isn't that long ;)

Male vocalists #1(clean):

1. Phil Lynott (Thin Lizzy)
Sooo cool :)
2. Marco Hietala (Tarot, Nightwish)
Beautiful voice, very variable.
3. Ian Anderson (Jethro Tull)
Smoothing and friendly voice. I especially like his movements at live performances :)
4. Warrel Dane (Nevermore)
Just great.
5. Bruce Dickinson (Iron Maiden)
The awesome voice of the best metal band in history.

I also like James Hetfield, Mikael Akerfelt, Rob Halford, Steven Wilson and Freddy Mercury very much.

Male vocalists #2(harsh vocals, screams, growls etc.)

1. Johann Hegg (Amon Amarth)
<33
2. Anders Friden (In Flames)
Used to be my favourite, but he kinda sucks since Reroute To Remain.
3. Tapio Wilska (Sethian, Finntroll, Nightwish)
Low and dark, clear pronounciation. Very nice.
4. Marcus Bischoff (Heaven Shall Burn)
Awesome brutal growling
5. Dan Swanö (Edge of Sanity)

Guitarists:


1. Jari Mäenpää (Wintersun, Ensiferum)
Amazing solos and songwriting <33
2. Gary Moore (Skid Row, Thin Lizzy)
+Phil Lynott = dreamteam no. 1 ))
3. John Petrucci (Dream Theater)
Just a great guitar player
4. Martin Barre (Jethro Tull)
Seriously the most underrated guitar player ever
5. Eric Clapton
Wrote wonderful songs

Guitarists I need to mention: Jeff Loomis - awesome solos, great riffs, Carlos Santana, James Hetfield - one of the best songwriters ever, Jesper Strömblad - writes awesome riffs and melodies, Empuu Vuorinen - nice melodic solos, Mikael Akerfelt

Feel free to leave a comment! =)