Off the top of my head, and admitting that I don't see the NL or west coast much:
4 Seamer: Papelbon. I'm biased as a Sox Fan but the guy strikes out a TON of batters and throws nearly 75% of his pitches as 4 seamers above the belt. When he's not rusty for lack of use, he pretty much just blows 4 seamers by guys over and over, throwing in the odd splitter and slider for a change of pace or for elite hitters. I watched almost every inning he pitched last year and I counted 3 times he gave up a square line drive off a fastball. It was incredible. Strange because he doesn't throw THAT hard (94-97). I think it's movement mostly, maybe something to do with his delivery and picking up the ball. The day I realized he was special was when I saw him throw 3 straight fastballs right over the middle past Sheffield, one of the best fastball hitters in baseball. On the last 2, Sheffield actually slipped to the ground he swung so hard. End of Papelboner rant. Sorry.
2 Seamer: No clue. It's hard to spot this pitch on TV and few play by play guys make the distinction. King Felix? I'm going to change this to sinker and say Lowe, Webb, or Wang. Take your pick.
Cutter: Still gotta be Mo right? Even though he is having an off year? Dunno. Pettite has made this his out pitch this season with a lot of success and Matsuzaka throws a half cutter half slider that he calls a "Shuuto" which is supposed to be pretty good.
Slider: K-Rod in my opinion, unless you call his pitch a cut fastball. Whatever. Randy still dominates and Smoltz throws a great one. Bonderman too. Those are a step above the rest I think.
Splitter: Clemens, hands down. This is how he is still getting by with a minimally used curve and a low 90's fastball. Schilling uses it as his main out pitch as well. So do a number of closers. AL east bias maybe.
Curve: Beckett, Peavy, Sabathia, Tom Gordon (still!), Sheets I watch Beckett every outing and his is so good it's scary. He can get by with a straight fastball, a good but not great change, and no 4th pitch because he throws hard and this thing is obscene. Mussina seems to have lost the feel for his knuckle curve. When he threw that for strikes he was tough.
Circle Change: Santana, Pedro. If Pedro can ever get healthy again, his is still the best, sorry Johan.
Straight Change: Hamels, Hoffman. Different pitch, with different movement, different velocity, and different arm action and grip. Less movement, more change of speed. Hoffman has lived on this pitch for 15 years.
Knuckleball: Wakefield, duh.