0302. Iron Butterfly
In-A-Gadda-Da-Vida

Iron Butterfly's name is a nice illustration of their sound: if it was just for the lyrics, they could have called the band Butterfly, since it's all about the love - trying to catch that special someone (and yes, since it's an album from '68 there are references to how "groovy" that someone is) - but with the addition of a proto-metal sound the fluttering butterfly gets heavy, cast-iron wings.

The first ever album to be awarded platinum status is a well deserving one where the tracks on the A-side all contains elements that, when combined, form the B-side spanning title-track. Like the lovelorn lyrics from Most Anything You Want and the repeated riff in Termination and of course the jam-influenced playing of Are You Happy.
The guitars are sufficiently fuzzed, the and the riffs' got hooks, but the clincher is Doug Ingle's organ-playing and voice - he sings the vocals like an Elvis of Doom instead of the gleeful cheer that the lyrics appear to have been written for.

Apart from having appeared on this list earlier as a bongo cover (though I seem to have missed to mention it) and further covered by everyone from Boney M to The Simpson's (and also sampled in a number of tracks), the seventeen-minute opus In-A-Gadda-Da-Vida is a staple in the music reference library as well as a damn good song.