Summer movie season usually means explosive action, jaw-dropping special effects and ultimately, big box office numbers.

But once in a while an unexpected hit sneaks up and gives the big guns a run for their money. Here's a look at five unexpected summer movie hits, dating back to 1998.

'My Big Fat Greek Wedding':This success story, penned by and starring then relative-unknown Nia Vardalos, had a shoestring budget of $5 million. But soon after its limited release in April 2002, the film caught fire over the summer months thanks to an enormous word-of-mouth campaign.

The comedy, which followed a strictly traditional Greek family's exploits as they prepared for their daughter's (Vardalos) wedding to a non-Greek suitor (John Corbett), ended up earning $241 million domestically and an additional $127 million overseas. To top the "Wedding's" cake, the film also earned Vardalos an Oscar nomination for Best Original Screenplay.

As luck would have it, Vardalos' next movie -- "My Life in Ruins" -- is set in Greece. Coming out in June, we'll find out if audiences are ready to celebrate with her again.

’Wedding Crashers": Another wedding movie party, "Wedding Crashers," was a big hit with moviegoers in 2005, as the modestly budgeted $40 million comedy starring Owen Wilson and Vince Vaughn took in $209 million in North American ticket sales.

Comedies generally do well at the summer movie box office, but the $200 million-plus take for "Wedding Crashers" elevated the film to its blockbuster status.

The movie, about a pair of buddies (Wilson and Vaughn) who unexpectedly find love at a wedding they crash, took in an additional $74 million overseas. Vaughn's love interest in the movie -- Isla Fisher -- would soon find love for real, with British actor-filmmaker Sacha Baron Cohen, who would turn America on its head in 2006.

'Borat': Even though the faux Kazakh journalist had been a staple on Sacha Baron Cohen's "Da Ali G Show," no one in the mock-documentary film saw the actor coming -- neither did moviegoers. The result was an uproarious $18 million-budgeted comedy that took in $128 million in North America.

Officially titled "Borat: Cultural Learnings of America For Make Benefit Glorious Nation of Kazakhstan." hoodwinked real folks into embarrassing situations, sometimes revealing the racially tinged underbelly of different regions in the U.S. Lawsuits followed but were effectively rejected, since nobody appeared to have read the fine print in the contract Baron Cohen had each of his "interview" subjects sign.

While "Borat" was a smash hit (it took in another $133 million overseas), apparently not enough people in the U.S. have the film's seen the film to recognize Baron Cohen and prevent him from doing it again. Baron Cohen will soon be back undercover again with "Bruno" where his "Da Ali G Show's" gay Austrian fashion guru fools the likes of the Alabama National Guard and former Republican presidential hopeful Ron Paul.

'Fahrenheit 9/11': Michael Moore's controversial acceptance speech for winning his Best Documentary Oscar for "Bowling for Columbine" in 2003 was a mere foreshadowing of his criticism to come of President George W. Bush. The full brunt wouldn't be dished out until the following year, where in June the documentary filmmaker released his scathing polemic "Fahrenheit 9/11."

Audiences undoubtedly wanted to hear what Moore had to say about the president's war policies post-9/11, which explains why the film -- budgeted at $6 million, grossed $119 domestically and $103 million overseas.

While the film was heaped with praise, starting with a standing ovation for Moore at the Cannes Film Festival, it was met with intense criticism, too, as well as documentary responses countering Moore's claims.

While the film was a box office winner, Moore would not get another shot at the Oscar podium to speak his mind. He submitted the film for Best Picture contention (it wasn't nominated), which took him out of play as a Best Documentary competitor.

'There's Something About Mary': The Farrelly Brothers -- Peter and Bobby -- became the kings of gross-out comedy in July 1999 with "There's Something About Mary," an uproarious comedy that catapulted Cameron Diaz's and Ben Stiller's careers into the stratosphere.

The film's $23 million budget was evidence that neither Diaz nor Stiller were commanding high paychecks yet, but that didn't prevent either one from delivering golden performances.

A comedy about a former high school geek (Stiller) who gets another shot at love with his high school crush (Diaz), the movie delivered hair-raising laughs with crude jokes about, among many other things, hair gel. While the movie was a smash at the domestic box office with $176 million in ticket sales, it was an even bigger hit overseas -- with a take of $192 million.