The summer transfer window is open now and MLS teams are already getting ready for what should be one of the busier transfer seasons in recent MLS history.

We aren't going to necessarily see teams splashing cash on millionaire transfer targets. However, with teams loading up for what should be an intense playoff race, effective transfer additions will be vital for teams with playoff--or even championship--aspirations.

Some have already fired their transfer window artillery, like the Montreal Impact (Marco Di Vaio and Alessandro Nesta) and New England (Jerry Bengtson), but those moves are just the beginning.

Here are five teams that could--and should--make moves this summer.

1. New York Red Bulls

The Red Bulls have an available Designated Player slot and a need for an attacking midfielder and third forward. RBNY GM Erik Soler insists the team wants to add a young DP, but rumors out of South America have linked the team with Argentine playmaker Riquelme (an appealing though unlikely option).

2. Chicago Fire

The Fire have the DP slot and money to make a big signing, with forward and attacking midfielder positions areas in which the team could upgrade. Names like Del Piero and Shevchenko have been thrown around, but it is tough to see Chicago overspending on an older option.

The Fire are also dealing with the potential departure of Marco Pappa via transfer, though that possible sale could help fund multiple summer additions.

3. Philadelphia Union

The Union already made a big summer addition with defender Bakary Soumare, but the team continues to have a glaring need for a marquee striker. The Union have the allocation money and cap room to sign one, but the question is whether interim head coach John Hackworth will pull the trigger on signing one or stick with the likes of Jack MacInerney and Lionard Pajoy.

4. Portland Timbers

The addition of Danny Mwanga was supposed provide a boost to an inconsistent attack, but the bigger concern is in midfield, where the Timbers have been thoroughly outplayed this season. Interim coach/GM Gavin Wilkinson needs to find a creative option in the middle, and you could argue the Timbers could stand to add a couple of midfielders.

5. Columbus Crew

It may sound like a broken record but the Crew still don't have an attack that can be considered playoff caliber. Columbus surely knows this and has already prepared for what is being called a significant summer signing. With forward Jairo Arrieta joining the team recently, you wonder whether the Crew try and find a strong central midfield upgrade.

Here is a rundown of this weekend's MLS matches to watch:

San Jose Earthquakes vs. Real Salt Lake

The Earthquakes are holding on to first place in the West right now but they will have a tough time holding onto it when they take on an RSL side that has Jamison Olave back from injury.

The battle between Olave and MLS goals leader Chris Wondolowski will be worth the price of admission but the game will likely hinge on the battle on San Jose's right flank. Chris Wingert must contain Marvin Chavez and keep Steve Beitashour from being too much of a factor.

For San Jose, Sam Cronin and Rafael Baca will need to make sure Javier Morales doesn't have too much room to operate. Do that and the Earthquakes can win and stay in first place.

New York Red Bulls vs. Seattle Sounders

The Sounders are starting to find a rhythm offensively, and Eddie Johnson is leading that charge with a strong run of form. Counting US Open Cup results, the Sounders are unbeaten in five straight against MLS competition.

The Red Bulls are heading in a different direction, with just one win in their past six league matches. Injuries continue to be a problem, but the team's back-ups aren't overachieving like they did earlier in the season.

If Thierry Henry is healthy enough to start then the Red Bulls are capable of knocking off the Sounders. Without him, the team's recent form just hasn't been good enough to suggest they can get more than one point without him.

Houston Dynamo vs. DC United

These East rivals meet for the first time since Houston won the opener at BBVA Compass Stadium in May. DC United has improved considerably since then, and the team is coming off a two-week break, so they should be rested and ready to push the Dynamo.

Chris Pontius has been particularly dangerous for DCU and should give Houston's right flank problems. As always, Dwayne DeRosario will be tough to handle, though Geoff Cameron could be assigned to try and lock down the MLS MVP.

For Houston, Brad Davis remains the focal point of the attack, and he gave United trouble the last time these teams met. Ben Olsen might consider a speedier option to deal with Davis, like Andy Najar.

Columbus Crew vs. Sporting Kansas City

Wednesday's US Open Cup semifinal victory should provide momentum for SKC heading into Columbus, but fatigue could play a role against a rested and defensively stingy Crew side.

Columbus is tough, but the team's inconsistent offense will have a hard time against a Sporting KC defense that was outstanding against the Union.

Portland Timbers vs. LA Galaxy

The post-John Spencer era begins in Portland, where the Timbers aren't that far off the playoff pace in the West. Beating the Galaxy at Jeld-Wen is a priority if they want to get back into the mix.

That won't be easy against an LA side growing closer to full strength. With David Beckham back from suspension, and Robbie Keane coming off his best game of the season.

The key for Portland is getting more out of a midfield that has been invisible in some recent games. If interim head coach Gavin Wilkinson can't find an effective midfield combination the Timbers could be on the short end against the Galaxy.