C Chord Progressions: Relative Minor Substitutions

Remember from last time:

I. C major
ii. Dm
iii. Em
IV. F major
V. G major
vi. Am
vii(b5). Bdim

Each major chord in the key of C has a relative minor that might sound great instead of playing the major chord, and vice versa. What? In other words...

I/vi: C major could possibly be substituted with Am
IV/ii: F major could possibly be substituted with Dm
V/iii: G major could possibly be substituted with Em

Instead of playing I-V-IV-I, for instance, try the following permutations (not an exhaustive list), but we'll start with the original progression:

I-V-IV-I: C G F C
I-iii-IV-vi: C Em F Am
I-V-ii-I: C G Dm C
vi-V-IV-I: Am G F C
vi-iii-ii-vi: Am Em Dm Am
etc.

Substituting a major chord with its relative minor (and vice versa) might liven up a boring progression with a less boring progression (albeit still widely used).