I used to love this place in 2005, but it just seemed to go downhill with each passing year. That being said, I really dig the setup. It's in an old warehouse type of space with lots of areas to sit and hangout on the side. They have a DJ every night playing a wide assortment of music (usually top 40 stuff on the weekends though) along with an area that turns into a dance floor as the night goes on. It's located on Mass ave half way between central square and MIT.
Middlesex Lounge