hahaha, frats. yes. that's where i come in. finally, something I can put my knowledge towards...yes!
*Note that this is all my personal view, and should not be taken as the true representation of any fraternity...I'm sure there are exceptions to every rule but I'ld hope that they would be a good start for the CC's here who are interested in fraternities. (Check out each fraternity's website if you're interested.)
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For even quicker overview, scores provided at the end for tameness/personality (of the people)/parties thrown (how big they are, how good they are)/level of presence on campus (people wearing the letters, representation at clubs, events sponsored, etc). (on scale of 1-5, 5 being the most untame/partiest/biggest presence)
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Alpha Delta Phi - located down Massachusetts Avenue, guys there are quite intellectual. Regularly places top 3 each semester for highest Greek GPA on campus. Haven't been to an open party although they do sponsor events occasionally. (1/?/2)
Alpha Epsilon Pi - Known nationally and locally as the Jewish fraternity, though not all brothers are Jewish. They've even sponsored a Bar Mitzvah party as a joke for a brother who never had one, so they do have their sense of humor. (1/2/3)
Alpha Tau Omega -Located on dorm row, they've been known to do some crazy stuff. If you go on collegehumor or youtube, you might find a picture of guys jumping out of their 5th floor windows into the snowpile beneath. Throws decent parties, although infrequent. Guys there are your more traditional frat boy types. (5/3/3)
Beta Theta Pi - Lots of tall, lanky, long haired, and um...experimental guys there. They're your skater type dudes around campus...can be lots of fun, they play in bands too. They have lots of low key pub nights, not so much large parties. (4/3/3)
Chi Phi - Bunch of nice boys, although you couldn't tell from the parties they throw. They live in this 16 million dollar governor's mansion across the river. The brothers are quite accomplished as well, from class presidents to international physics scholars. Though, don't get the wrong impression, they're very down to earth and approachable. (3/5/4)
Delta Kappa Epsilon - Currently restructuring due to past violations (so not much to say). Although, I believe they still rush... (5/?/?)
Delta Psi/No. 6 - It's a co-ed fraternity. Lately, many international students from Europe has joined the living group, giving it much diversity. Throws good parties occasionally as well, although not widely publicized. (2/4/2)
Delta Tau Delta - They're your charismatic, recently turned "frat boys with a heart of gold". Filled with swimmers, divers, and a cappella singers...a.k.a. they're athletic, musical, and charming...no wonder a popular hit among the ladies. Did I mention they throw ridiculously large and crazy parties at least twice a semester? (4/5/5)
Delta Upsilon - Your pretty boy frat. Reputation among girls have fallen quite a bit in recent years. Pub nights regularly and throw occasional parties. (4/4/3)
Kappa Sigma - On dorm row. Don't know much, but I get the impression that the people are very similar to those Alpha Tau Omega...(they ARE right next to each other)... (5/3/2)
Lambda Chi Alpha - Lots of jocks. Lots of drinking. I may be stereotyping though...Not everyone's like that though. It's unfortunate that they don't do more to change that impression on campus. (5/5/3)
Nu Delta - Your cool, chill guys. They're pretty cohesive as a fraternity, and have pretty good relations with other fraternities and sororities. (4/4/4)
Phi Beta Epsilon - They're probably your largest frat right now. Had an excellent rush year last year, got 27 pledges. Always known for throwing excellent dance parties on their roof deck. Includes some accomplished individuals, although you wouldn't know by looking at them. (4/5/5)
Phi Delta Theta - They have some nice and friendly brothers. They'll say hi to you in the halls even though you may have only met once. The guys are usually well known and popular around campus, and the fraternity has quite good connections with the sororities as well. (3/4/5)
Phi Kappa Sigma - A.K.A. Skullhouse. Don't worry, they're not as scary or secretive as they sound. Although, if you're a girl, a couple guys there might sketch you out

. Pretty harmless though. They might seem like they don't work very hard academically, but they really have some smart guys there. (4/3/2)
Phi Kappa Theta - A "nice guy" frat. Girls would describe the guys there as sweet and gentlemen like. Good working relationship with other frats and especially sororities here. (3/3/5)
Phi Sigma Kappa - Pretty down to earth and approachable guys who like to have fun also. Located right next door to and across from sororities, they're excellent hosts especially known hosting some event for the Boston Marathon each year. (3/3/4)
Pi Lambda Phi - The guys there are pretty tame, and they're not afraid to show their nerdy/dorky side. (1/2/2)
Sigma Chi - Outgoing guys, got a couple guys popular among the ladies. Kinda goofy. You'll usually find as many if not more BU and Wellesley girls there than MIT girls. (4/3/3)
Sigma Nu - Lives next to the Berklee School of Music, the guys there are very sweet with a gentlemen side to them. Wellesley girls visit a lot. (3/3/2)
Sigma Phi Epsilon - Restructuring, although, I'm quite impressed by the outstanding citizenship of the guys. Even though they got into some trouble a while back, I quite respect each brother that I have met in terms of personality, academics, and other various accomplishments. (3/?/3)
Tau Epsilon Phi - These are the guys in purple jump suits. I believe it has broke with national rules and have become co-ed? The guys there are very much like your explosion loving, science experimenting, EC/Senior House types. (5/?/3)
Theta Chi - Again, I apologize as I haven't visited this fraternity since Freshmen year...so in my head, I group them with Sigma Chi.(4/3/3)
Theta Delta Chi - Like Beta Theta Tau, but on campus, and shorter guys. (4/2/2)
Theta Xi - They're rather accepting of the alternative lifestyle. The brothers are pretty involved in their frat and are pretty close. They do throw parties occasionally through out the year. (3/4/3)
Zeta Beta Tau - Your smart, nerdy, sweethearts. Good working relationships with sororities. (2/4/4)
Zeta Psi - Your nerdy guys with a crazy side. (Occasionally throw large parties, smash cars, etc). (3/4/3)
Rush starts right at the end of orientation. At a Greek barbeque kick off, frats will just grab you and take you to their houses and events. But hopefully, this list will give you a good start on your search.