Major 7th chords
Top a major triad with a major seventh instead of a minor one and the chord stays inside its own key rather than pulling anywhere. The result is warm and reflective, a little more sophisticated than a plain triad, and it shows up constantly in soul, bossa nova and any film cue that wants a major chord to sound thoughtful rather than triumphant.
Other chord types
MajorMinorDiminishedAugmentedSuspended 2ndSuspended 4thDominant 7thMinor 7thMajor 6thMinor 6thMinor Major 7thDiminished 7thHalf-Diminished 7thAugmented 7thAdd9Dominant 9thMajor 9thMinor 9th6/9Dominant 11thMinor 11thDominant 13thMajor 13thMinor 13th7sus47b57b97#9Dominant 7#11Minor 6/99sus4Power Chord (5)Minor Add9Add117sus213sus4Minor Major 9thMajor 7#11Major 9#117b1313b913#117altAugmented Major 7thMinor 9b5Quartal (So What)