Here’s an interesting progression found in a number of songs. Listen to Lee Brice’s song Love Like Crazy to hear it (see Youtube video at the end of this post).

The example in the key of G is G, Gmaj7, G6, Gmaj7 and then repeats:

G-Gmaj7-G6-Gmaj7

Now try it in the key of D:

D-Dmaj7-D6-Dmaj7

Listen to what the progression sounds like in Lee Brice’s song here: