The first one is primarily just 7 minutes of Trixie, not really a complete song, but several mixed jingles.
The 2nd, 3rd, and 4th are a bit more specified.
1.) The Great and Powerful Trixie
2.) Applebuck Season - Twilight's Speech
3.) Once Upon a Time in Equestria (Episode 1 Opening)
4.) Celebration of Harmony (Episode 2 Conclusion)