Code Geass second ending-> http://www.youtube.com/watch?v=Ejxess2b8aY

I can't remember much but here's some from the top of my head. DRRR's ending, Guilty Crown's 'My Dearest' and 'The Everlasting Guilty Crown' and Natsume Yuujinchou's music too. As for soundtracks, I love the ones from Tsubasa Chronicles

Death Note opening and endings
kuroshitsuji openings and endings

There are many theme songs that i like ;D

-I like all the openings and ending from Kuroshitsuji
-Core Pride (AnE)
-Yokan (kaichou wa Maid-sama)
-Key (Shinrei Tantei Yakumo)
-Oprheus Heart (Uta no Prince-sama)
- and of course the Death Note Songs ;D
-The magi Opening ;D

I didn't really start paying attention to theme songs until I met my boyfriend and I'm so glad I do now! Before they were always just kinda there but now I actually notice them and it's so cool.

I love all the K-On! songs. I actually downloaded some of them. The Clannad ending theme was adorable so, of course, I downloaded that one too.

Hm... So many good OPs... I'll just list a few.
Only My Railgun (A Certain Scientific Railgun)
88 (Kateikyoushi Hitman Reborn)
Colors (Code Geass)
Change (Bleach)
Crossing Field (Sword Art Online)
Innocence (Sword Art Online)
Stone Cold (Sacred Seven)
Sousei no Aquarion (Sousei no Aquarion)
Hishoku no Sora (Shakugan no Shana)
Oath Sign (Fate/Zero)
VIP (Magi- Labyrinth of Magic)

There are also tons of good insert songs, though I guess I'll leave 'em out, since this thread is about OPs. I also recommend looking up some game OPs, though I'll leave those out too P:

The opening to Baccano is amazing! I love the original openings to both soul eater and fma as well.

Gee, erm...

I like the openings to these series:

Re:Cutie Honey- Mostly because I absolutely love the animation style and the song is nostolgic to me. Link: (May not be appropriate for younger children... There's no nudity but... Lots of ripping and tearing of clothes. :P) http://www.youtube.com/watch?v=yM9_WHbm3OE

Getsumen No Heiki Miina (Aka: Lunar Rabbit Weapon Miina)- For some reason, I'm really attracted to this song... It starts out a bit oddly pitched but I find myself humming the chorus of this theme song to myself at times. Link: http://www.youtube.com/watch?v=3pAhIU9QK0k

Also, this is an ending to an OVA of one of my favorite comedy mangas but it's so extremely random so I thought you might want to hear it...
Link: http://www.youtube.com/watch?v=oAdr94fzNPA
The anime is Dragon Half which is a fantasy-adventure spoof and It's just... Well... Random to hear the main character Mink singing about Eggs and tomatoes...

Other openings I like:
Spice and Wolf Season 1 OP
Windy Tales OP
Astarotte No Omocha OP
Urusei Yatsura OP

Geez, this turned about to be a long post...

My favourite list
-ghost in shell opening
-some naruto songs
-last exile opening and ending
-all fma songs
-fantastic children opening