I'd like to add the opening/ending list to this thread, mainly to avoid people from doing threads just to ask "What's the ending after xx ending?" or "How many openings One Piece has so far?". Well, all our questions regarding the Openings and Endings shall be answered now:
Openings:
1. We Are!, by Hiroshi Kitadani (episodes 1-46)
2. Believe, by Folder5 (episodes 47-116)
3. Hikari E, by The Babystars (episodes 117-168)
4. Bon Voyage!, by Bon-Bon Bianco (episodes 169-?)
Endings:
1. Memories, by Maki Otsuki (episodes 1-30)
2. Run! Run! Run!, by Maki Otsuki (episodes 31-63)
3. Watashi Ga Iru Yo, by Tomato Cube (episodes 64-73)
4. Souchinosuke, by Suitei-Shoujo (episodes 74-81)
5. Before Dawn, by Ai-Sachi (episodes 82-94)
6. Fish, by The Kaleidoscope (episodes 95-106)
7. Glory ~Kimi Ga Iru Kara~, by Takako Uehara (episodes 107-116)
8. Shining Ray, by Janne d'Arc (episodes 117-129;131-132)
Special 8. Family, by The Straw Hat Pirates (episodes 127-128)*
9. Free Will, by Ruppina (episodes 133-155)
10. Faith, by Ruppina (episodes 156-168)
11. A to Z, by ZZ (episodes 169-181)
12. Tsuki to Taiyou, by Shela (episodes 182-195)
13. Dreamship, by Aiko Ikuta (episodes 196-?)
*This ending aired on a double episode special (127-128), which were the last episodes of the Arabasta arc. It's sung by the One Piece Straw Hats seiyuu team (Mayumi Tanaka; Kazuya Nakai; Kappei Yamaguchi; Hiroaki Hirata; Akemi Okamura; Ikue Ohtani; and Misa Watanabe).
Additional Themes: Movies and Specials
Movie 1 - One Piece The Movie
Opening- We Are!, by Hiroshi Kitadani
Ending- Memories, by Maki Otsuki
Movie 2 - Adventure on Nejimaki Island
Ending- Believe, by Folder 5
Movie 2 short - Jango's Dance Carnival
Ending- Ready!, by Folder 5
Movie 3 - ?
Ending- Mabushikute, by DASEIN
Movie 4 - ?
Ending- Sailing Day, by Bump of Chicken
Special 1 - The Ocean's Bellybutton
Opening- Believe, by Folder 5
Ending- Run! Run! Run!, by Maki Otsuki
Special 2 - ?
Opening- Hikari E, by The Babystars
Ending- Free Will, by Ruppina
Special 3 - ?
Opening- Bon Voyage!, by Bon Bon Bianco
Ending- A to Z, by ZZ
Whenever a new ending or opening begins, I'll try to update the list
PS. Sorry for the double post, but it was obviously necessary.