A lot of great guitarists being mentioned here (RestorationAD got a lot of it right) but I feel a few has been lost to the Rush debate
My all time favorite will always be Slash - great, catchy leads, good tone/timbre, lovely hat.
Other guitarists worthy of mention:
Steve Lukather
Richie Kotzen
John Mitchell (Arena, Kino, Frost, It Bites)
Joey Eppard (3) - Unique style
Daniel Gildenlöw (Pain of Salvation)
Mattew Bellamy
Roine Stolt (Flower Kings, Transatlantic, Agents of Mercy)
Adam Jones (Tool)
Mikael Åkerfeldt (Opeth)