Due to popular demand I've decided to make this public. It's my list of music-works that are essentially free to use (commercially and non-commercially), by virtue of either being a folk-song (and thus belonging to "the folk"), or because they are so old they precede copyright and are generally accepted as public domain. This can help save you a lot of time when scouting for music to use in your film/game/podcast/etc.
I have compiled this over several years, and add interesting titles whenever I stumble upon them. Since I picked these from all kinds of different places there are no unified sources.
While a certain title might be public domain, most modern recordings are NOT. Kilgary Mountain is free to use, Metallica's cover Whiskey In The Jar is not.
Due to this I advise just creating an own version. It is possible to create something reasonable with simple audio-software (i.e. Guitar Pro) and some sheet-music.
I take no ultimate liability for this information. It is supposed to point you in the right direction. While I am fairly sure of the availabitly of these songs, I implore you to check for yourself. In which case you might very well end up saving a huge amount of time and/or money anyway.
This list is by far not final. In fact there are tons of more pieces, these are the more "popular" ones. Go dig through some Chopin-CDs for the truly underused (und underrated) stuff.
There are few games with a primarly classical soundtrack (Flotilla, Unstoppaball DX). Other games often add these in a few places. In Vampire: The Masquerade: Bloodlines, for example, a "high class"-character has some Beethoven running in his room.
Auld Lang Syne
Oh Danny Boy
Whiskey in the Jar
Bach - "Little" Fugue (G minor, BWV 578)
Bach - Brandenberg Concerto No. 3 - Allegro(1721)
Bach - Brandenburg Concerto No. 3
Bach - Concerto No. 4 in A
Bach - Concerto No. 5
Bach - Fantasy and Fugue
Bach - Partita No 1. - Gigue
Bach - Toccata and Fugue in D Minor
Beethoven - Egmont Overture
Beethoven - Für Elise
Beethoven - Piano Sonata No. 14, "Moonlight Sonata", First Movement: Adagio sostenuto *
Beethoven - Sonata No. 14 "Moonlight", 1st Movement.
Beethoven - Sonata No. 14, 3rd Movement.
Beethoven - Sonata No. 23 "Appassionata", 1st Movement.
Beethoven - Symphony No. 1, Finale
Beethoven - Symphony no. 5 in C Minor: Allegro
Beethoven - Symphony No. 5 in C Minor: Allegro con brio
Beethoven - Symphony No. 5, 1st Movement.
Beethoven - Symphony No. 6 "Pastoral", 1st Movement.
Beethoven - Symphony No. 9, 4th Movement.
Beethoven – Symphony No. 7, 4th Movement: Allegro Con Brio
Bizet - Les Toreadors
Bizet – Habanera
Boccherini - Minuet
Brahms - Hungarian Dances No. 5
Chopin - Ballade No. 1
Chopin - Concerto No. 2, 1st Movement.
Chopin - Concerto No. 2, 3rd Movement.
Chopin - Etude No. 11
Chopin - Etude No. 3
Chopin - Impromptu
Chopin - Prelude No. 15
Chopin - Prelude No. 17
Chopin - Prelude No. 3
Chopin - Waltz No. 6
Chopin's 'Funeral March
Delibes - "Flower Duet" from Lakme
Dvorák - Humoresque Op. 101 No.7
Dvorak – New World Symphonie
Dvorák: Symphony No. 9 "From the New World"
Grieg - Hall of the mountain king
Grieg - Peer Gynt Suite No. 1 - "In the Hall of the Mountain King"