Rock Band 3
The ultimate in party game technology, Rock Band 3 took everything that Harmonix had learned about rhythm games from making Guitar Hero and two Rock Band titles, and threw it all onto one disc -- and it was AWESOME. Getting friends together always meant music, no matter how many of you there were. You could swap players in and out, sing up to four-part harmonies, and even set that game up in a party mode that constantly played music, whether or not someone was actually playing. year of DLC support meant that you could play tons of your favorite songs with your friends, no matter how bad you were as a musician. If you were actually talented, pro mode would up the ante and let you take on the music as it was meant to be played. Harmonix has recently begun discussing the possibility of a sequel, and released their first Rock Band 3 DLC in two years, so maybe Rock Band 4 is on the way. If so, it'll likely be a great one to play with friends as well.