I like Dominant 7th chords. They are cornerstones for the styles of blues and jazz, and they pop up everywhere in between. Major 7th’s and minor 7th’s conform to the diatonic scale, but dominant 7th’s are just too cool to hang out with that crowd. Theory-wise, a dominant 7th chord is essentially a major triad that stole a minor 7th and got away with it!
Welcome to the land of dominant 7th’s!!! There are many more but this should give you a good head start:
(Note: many of these are inversions so look carefully before memorizing)