The midpoint of the 2009 MLS season, conveniently enough, dove-tails with the start of summer, and thus a staggering load of international competitions and friendly matches.

Four MLS teams are involved as SuperLiga kicks off this weekend, the Gold Cup will jumble rosters starting in early July, more than a half-dozen foreign teams will swing through MLS cities playing league teams as well as each other, and in late July the Concacaf Champions League group phase will commence with five MLS entrants.

Roster changes are imminent with the MLS contract guarantee date looming, and the domestic transfer window set to open July 15. So the first half of the league season won't much resemble what follows, but for the past three months, these are the players who have been essential to their teams' success.

GOALKEEPER
Zach Thornton (Chivas USA)
The big man leads the league in saves and is just behind Pat Onstad of Houston in goals-allowed average. Coach Preki would no doubt like to cut down on the number of good chances his team is allowing and rely less on Thornton's excellent goalkeeping as it duels with the Dynamo for the conference title.

DEFENDERS
Geoff Cameron (Houston)
While Coach Dominic Kinnear has resuscitated the careers of strikers like Kei Kamara and Cam Weaver with Svengali-like effect, he's also quietly transformed this wide midfielder into one of the league's best central defenders. Fast, smart, strong in the tackle and good on the ball, Cameron is still learning the position. That's a lot of upside.

Mariano Trujillo (Chivas USA)
A smart, reliable defender, his offensive abilities going forward have compensated greatly for the indifferent form of Sacha Kljestan. The veteran of more than a decade in the Mexican league is just 32 and seems capable of locking up this position for a few more years.

Wilman Conde (Chicago)
A monster in the air and a decent passer, Conde has been steady in the back for a Fire team blessed with talent but plagued by inconsistency.

MIDFIELDERS
Guillermo Barros Schelotto (Columbus)
Led the league in assists last year and so far leads the league in goals, which is what a number 10 is all about. Brings incredible vision and class to a hard-working team, and puts attacking teammates in the best possible situations with his touches and passes. MVP Redux? Maybe.

Shalrie Joseph (New England)
Played a few games up front to help an injury-ravaged team. Is often asked to fill two or three roles at various points of a game as the Revs try to grind out points as players get healthy.

Stuart Holden (Houston)
Settled into a central role after laboring the first month of the season while also playing out wide. Can lead the attack in an advanced position or join up from behind the first wave. Very smooth on the ball, a good passer with both feet, and poised under pressure, he's blossoming into one of the league's best midfielders.

Osvaldo Alonso (Seattle)
An excellent tackler with good range, Alonso has given the expansion Sounders a midfield hub good on the ball who can also distribute. He showed his shooting skills by belting a long-range shot into the top corner against D.C. United and should be a strong contributor as he adds more league matches and international contests to his resume.

Santino Quaranta (D.C. United)
He would be a good choice on sentimental grounds for overcoming a drug dependency, yet Quaranta's menacing, confident attacking play is a primary reason opponents have been unable to put away United. Whether or not his touch is at its sharpest, he goes at foes on and off the ball, and does a fair bit of defensive work as well.

FORWARDS
Conor Casey (Colorado)
Has formed a nice partnership with Omar Cummings and gives Colorado a big man in the box who can set up chances as well as put them away. International experience at the Confederations Cup should aid him and the Rapids down the stretch. He's on pace to score 15 goals, which no Colorado player has ever accomplished.

Brian McBride (Chicago)
A threat to win the ball, set up a chance, or go for goal every time the Fire gains possession and moves upfield. His experience will be essential as teammates come and go on international duty; his presence and finishing ability gives Chicago elements critical to winning tight games.

Reserves: Onstad (Houston), Chad Marshall (Columbus), Dejan Jakovic (D.C. United), Steve Ralston (New England), Brad Davis (Houston), Kyle Beckerman (Real Salt Lake), Chris Pontius (D.C. United).

Who are YOUR picks for the best MLS players of the first half of the season? Let us know below.