There are still a few successful players who throw the knuckleball. There never has been a large number of players to use the knuckler regularly, giving it the reputation as one of the strangest pitches in baseball. Here are a few who are still in the game.
Tim Wakefield is probably the most well-known current knuckleball pitcher. He has been in the majors since 1992 and will likely end the 2011 season with 200 wins. He's becoming a player with an ERA between 4.00 and 5.00 who is good for about 120-140 innings a season. Most teams wouldn't mind calling him their #4 or #5 starter but he probably only has a couple years left as a starter.
Other Pitches: This season Wakefield has thrown his knuckleball about 90% of the time with his fastball and a cutter of sorts accounting for the other 10%.
Dickey was drafted in '96 and has played for five different teams. He really made himself known last season (2010) when he won 11 games for the Mets with a 2.84 ERA. This season he has not had the same success but has been a good starter for New York.
Other Pitches: Dickey has thrown his knuckler 77% of the time in 2011, a slight decrease from 2010. His other pitch is a fastball which averages about 84 mph. Earlier in his career he threw a changeup but stopped throwing that last season.
Haeger was drafted by the White Sox in 2001 and made the majors in 2006. He hasn't found consistent success and is currently playing in the minor leagues for the Los Angeles Dodgers. His performance has been steadily decreasing the past few years.
Other Pitches: Since Haeger hasn't played in the majors in 2011 there is little pitch data for him. In 2010 however, he used his knuckler only 59% of the time and mostly his fastball and curveball the rest of the way.
Bonine has pitched 129 innings at the major league level with moderate success: 4.74 ERA, 1.54 WHIP. He was recently granted free agency by the Detroit Tigers and was signed by the Phillies. He's currently pitching for AAA Lehigh Valley and sports an ERA over 5.00.
Other Pitches: Bonine has never thrown his knuckler exclusively. In fact, only about 12% of his pitches in 2010 (at the ML level) were knuckle balls. He didn't throw any of his pitches more than 20% of the time, relying on a variety of pitches.
There is only one knuckleballer in the minors that I know of: Houston Summers. Summers is in low-A ball with the Cardinals after a run with the Diamondbacks.
There are never many knuckleball pitchers in the majors at one time, but there are never zero either. Something tells me this short list of current knuckleball pitchers will still be playing pro ball next year as well.