I wanted to do this a while back, but there are many anime opening and ending themes that I like so much that they rank among my favourite songs. So I'm going to list every anime theme that I've found decent enough to put on my mp3 player at some point, and from them I'll select my top 10. I do have Full Moon themes, but they never made it onto my mp3 player =P more because I couldn't be bothered than actually disliking them. By the way, just because I have the opening/ending theme of an anime, doesn't mean I like it or have watched it. I'm mainly referring to Vampire Knight (re the first) and Koutetsu Sangokushi (re second).
Oh, and these are just my opinions. If you don't like the song or like a song that's not listed, don't go 'urgh that's a crap song, this song is so much better' cos chances are I have no idea what song you're talking about.
Casting Dice -- Amatsuki opening
Namae Nai no michi -- Amatsuki ending
Be My Angel -- Angelic Layer opening
Starry Sky -- Angelic Layer ending 1
Catch You Catch Me -- Cardcaptor Sakura season 1 opening
Groovy -- Cardcaptor Sakura season 1 ending
Tobira wo Akete-- Cardcaptor Sakura season 2 opening
Honey -- Cardcaptor Sakura season 2 ending
Platinum -- Cardcaptor Sakura season 3 opening
Fruits Candy -- Cardcaptor Sakura season 3 ending
Tsubasa wa Pleasure Line -- Chrno Crusade opening
Sayonara Solitaire -- Chrno Crusade ending
Mag mel ~cuckool mix 2007~ -- Clannad opening
Chiisana Te no Hira -- Clannad movie ending
Toki wa Kizamu no Uta -- Clannad ~After Story~ opening
Colors -- Code Geass opening 1
Kaidoku Funou -- Code Geass opening 2
World End -- Code Geass RS opening 2
~Byakuya~ True Light -- D.N.Angel opening
Hayate no Gotoku -- Hayate no Gotoku opening 1
Shichitenhakki Shijou Shugi -- Hayate no Gotoku opening 2
Kono me kaze -- Hayate no Gotoku ending 4
Last Regrets -- Kanon 2006 opening
Kaze no Tadori Tsuku Basho -- Kanon 2006 ending
Kuon -- Koutetsu Sangokushi ending
Monochrome no Kiss -- Kuroshitsuji opening
Kimi + Boku = Love? -- Lovely Complex opening 1
~Kiss~ Kaeri Michi no Love Song -- Lovely Complex ending 1
Sakura Kiss -- Ouran High School Host Club opening
Shissou -- Ouran High School Host Club ending
Kimi to Deatte Kara -- Princess Princess opening
Hohoemi wo Agetai -- Princess Princess ending
OK -- Pokemon Gold and Silver opening
Find Out -- Switch OVA opening
Your Hand -- Switch OVA ending
Gorgeous 4U -- Special A opening 2
Hidamari no Gate -- Special A ending 1
Bouken Deshou Deshou -- Suzumiya Haruhi no Yuutsu opening
Hare Hare Yukai -- Suzumiya Haruhi no Yuutsu ending
Blaze -- Tsubasa Chronicle season 1 opening
aerial -- Tsubasa Chronicle movie opening
IT'S -- Tsubasa Chronicle season 2 opening
Synchronicity -- Tsubasa Reservoir Chronicle: Tokyo Revelations opening
Saigo no Kajitsu -- Tsubasa Reservoir Chronicle: Tokyo Revelations ending
Futatsu no Kodou to Akai Tsumi --Vampire Knight opening
19sai -- xxxHolic opening
Reason -- xxxHolic ending 1
Kagerou -- xxxHolic ending 2
Sanagi -- xxxHolic Movie opening
Kiseki -- xxxHolic Movie ending
Nobody Knows -- xxxHolic Kei opening
Honey Honey -- xxxHolic Kei ending
Final Results
1. ~Byakuya~ True Light --D.N.Angel opening
2. BLAZE -- Tsubasa Chronicle opening 1
3. Find Out -- Switch OVA opening
4. World End -- Code Geass R2 opening 2
5. Toki wa Kizamu no Uta -- Clannad After Story opening
6. Monochrome Kiss -- Kuroshitsuji opening
7. Colors -- Code Geass opening 1
8. 19sai -- xxxHolic opening
9. Your Hand -- Switch OVA ending
10. Casting Dice -- Amatsuki
~Byakuya~ True Light is number one because it's just beautiful. I'm in love with the piano version too XD.
BLAZE gets number 2 because... well I just love it. I guess it's cos I can feel the meaning of the words inside the music. It's really inspiring if I'm feeling down
Find Out, World End, and Colors are listed because of the level of adreline rush they give me.
Toki wa Kizamu no Uta is #5 because it's a beautiful song. Also it's one of the saddest songs that I've ever heard. Nearly made me cry the first time I heard it
Monochrome Kiss, Your Hand and Casting Dice are just awesome songs XD
19sai when I think of it, I think of the xxxHolic anime, so it's got good memories attached to it XD
Honourable mentions:
Catch You Catch Me because it is the classic among anime songs
Tsubasa Wa Pleasure Line because it's very awesome. It was seriously like half a step away from Casting Dice
Sayonara Solitaire is the second saddest song I have, and I love it a lot