(1-4)   A simple two chord progresssion. Examples below Feelin’ Alright (Joe Cocker), Imagine (John Lennon).  The repetition of two chords can be used to create a tension or anticipation of more to come, which may then be resolved in the chorus.

The ausio  sample here is in the key of A, using A and D chord variations.

Joe Cocker - Feelin' Alright

This one is in the Key of C.  Chords used: C7, F7. 

R.E.M. - Everybody Hurts

This song is in the key of D.  The beginningof each verse uses chords I and IV,  D and G.

John Lennon - Imagine

This track is in the key of C. Each verse has just chords C and F before the pre chorus.

Other Examples of this Progression

Kenny Rogers & Dolly Parton - Islands in the Stream (verse)

Paul Simon - Loves me Like a Rock (verse)