The Minor Pentatonic Scale
Scale formula: 1, b3, 4, 5, b7. Every guitarist needs to know the minor pentatonic scale. It's always been at the heart of most blues and rock soloing, whilst jazz players like to get all sophisticated by superimposing the scale over various chords for all kinds of interesting sounds. Many people find all they need in the first couple of patterns but you'll definitely be a more versatile player if you learn and can make music from all 5 shapes.