If this will be your only suit, I would get a very dark navy or charcoal solid (echoing what others already wrote), and definitely not get anything trendy (what DeltAlum wrote.) I recomend a Brooks Brothers suit, as they are very well made, and are guaranteed indefinitley (unless you bring it back with huge holes.
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If you get a three button jacket, make sure that the top button is not visible when the lappel is in the standard positon. This is traditional. The purpose of the third, and top button, is to hold the lappel up when you get caught in nasty weather without an overcoat.
ETA A blazer and khakis may be more appropriate. I'd ask some brothers of the fraternity that you are joining. The advice on three buttons still applies.
Also, not only single breatsed, but also vented.
Threaded Mode