I never actually played Maniac Mansion when it originally came out, but in 1993 when playing its sequel Day of the Tentacle. You see, when you use a certain Commodore 64 in the game, it actually boots up the original Maniac Mansion which is pretty awesome since you get two games for the price of one!
Maniac Mansion had surprisingly funky music considering its raw 8-bit sound - which goes to show how talented the composers were (Chris Grigg and David Lawrence I believe). My personal favourite is Flashbulb Funk (Michael's Theme) although there are a couple of other good ones too, including the main theme.
Here it is in all its 8-bit glory.