favorite anime opening?

[Eternally Euphoric]

Going to second Nekodog on this one,

Full Metal Alchemist Brotherhood's Again by Yui is still stuck in my head today.

I also love the 2nd OP in Durarara, I believe it was Complication by ROOKIE'z iS PUNK'D.

Same with Ao No exorcist for both OPs, core pride and in my world were both great tunes.

[Angel of hororr]

My favorite opening is Durarara's 2nd - Complication.

[JediPadawanJess]

Pegasus Fantasy by Make-Up (Saint Seiya)
We Are by Vic Mignogna (One Piece)
Tsubasa wa Pleasure Line (Chrono Crusade)
Sorairo Days by Shoko Nakagawa (TTGL)

[Pink_Frosting5]

Again by YUI from FMA is pretty good.
Code Geass also has some really good openings and endings.

[VictoriaVictimizer]

Fruits Basket, Black Butler, Chobits, Ben-To

[nuffie91]

The first one that comes to mind is Haganai.
So catchy and adorable 3nodding

[Viege]

Blue Seed

Serial Experiments Lain

Gundam Wing

[astroblook]

Just to name a few off the top of my head:
This Game (No Game No Life)
Unravel (Tokyo Ghoul)
Crossing Field (SAO)
Complication (Durarara!!)

[Red Erika]

I always liked Cowboy Bebops opening and R.O.D. TV...