Fm, F major, Ab major or Am
All of these chords would 'work' in C major, especially vi (Am) which is the famous Aeolian Cadence (Ticket 10).
If you use extended chords the options increase. The easiest way to think about this is adding the tonic note into each chord. For example (again in C major).
If you're happy for your melody to land on something other than the root note, the choices are infinite.
As with the Picardy, you can use this trick to end a section (Something), or the whole song (And I Love Her).
It's an art to finish well on something other than the root chord.
A root chord say “THE END” or “FULL STOP (PERIOD)”.
Picardy Third says “SURPRISE HAPPY ENDING!”
The tape cut off ending, whether accidental (Her Majesty) or deliberate (I Want You She's So Heavy) says “HEY THE LAST PAGE IS MISSING DAMMIT”.
Anything else may just say “TO BE CONTINUED...”
1963 Ask Me Why - The Beatles (2:16) - iii
1964 When I Get Home - The Beatles (2:02) -VI
1964 And I Love Her - The Beatles - VI
1965 And Your Bird Can Sing - The Beatles - IV
1965 You've Got to Hide Your Love Away - The Beatles - V
1966 For No One - The Beatles - IV of minor key bridge, or V of major key verse
1968 Let's Make the Water Turn Black - Mothers of Invention – VI
1968 Piece of My Heart – Janis Joplin - ii
1969 Because - The Beatles (0:00) - bii dim
1969 Something - The Beatles (2:45) - VI
1969 Badge – Cream - iv (Em) or v (D mixolydian)
1970 25 or 6 to 4 – Chicago - II/I
1973 The Ocean – Led Zeppelin - V
1971 Wind-Up – Jethro Tull - V
1976 Silly Love Songs - Wings - iii
1980 Steeler – Judas Priest (4:14) - bVII
1980 Lately – Stevie Wonder - VI
1985 Against All Odds (Take a Look at Me Now) - Phil Collins - V
1995 New Test Leper – R.E.M. - ii
Ticket 1: The Flat 6 Chord
Ticket 6: Stay Off The Root Chord
Ticket 8: Use The Minor 4 (iv) Chord
Ticket 10: The Aeolian Cadence
Ticket 13: Make The Vocals Stay On Non-Chord Tones
Ticket 14: Write An In-Key Melody Over Out-Of-Key Chords
Ticket 16: The Picardy Third
Ticket 18: Finishing On A Single Ringing Chord
Ticket 28: Use At Least One Out Of Key Chord
Ticket 44: Use the Minor 5 (v) Chord
Ticket 45: Change Keys Between Sections
Ticket 47: False Ending
Ticket 49: Employ Madrigalism
See the full list of songwriting tips here - Tickets To Write