I don't want to put something anyone else has put, but there's a lot I like. Ash Like Snow (Gundam 00 OP2) is one of my favourites.
Tsubasa Wa Pleasure Line - Chrno Crusade OP
http://ca.youtube.com/watch?v=KvtxV7Zvjp0
It really shows the emotions between the two main characters. And the song is catchy too.
Friends - Gundam 00 ED 2
http://ca.youtube.com/watch?v=2MOycSJhp5c
I swear I like this for more than the half-naked Allelujah. I like that it shows the pilots interacting and relaxing, but it also shows the sadder aspects of the series.
Faith - Rental Magica OP English Version
http://ca.youtube.com/watch?v=UmgRuk...eature=related
It's a nice song and I like the video; it comes with karaoke lyrics int he video
Romantic Morning - Kyou Kara Moau R (OVA) OP
http://ca.youtube.com/watch?v=Dw3A0cBaiYg
It's so peppy. I can't help but bounce to it.
Keseki no Umi - Record of Lodoss War OP
http://ca.youtube.com/watch?v=KNYi6CGVdaY
It's an older anime but the song is nice and the video is nostalgic.
Wind - Naruto ED 1
http://ca.youtube.com/watch?v=VyGx0yJsJfA
I always thought this reflect Naruto's character, and the song is so sad sounding
Distance - Naruto Shippuden OP2
http://ca.youtube.com/watch?v=qy3HHnF8xPk
I know another Naruto song; but it really reflects Naruto and Sasuke's relationship. (ignore the subbers comments ^^U)
Hit in the USA - Beck Mongolian Chop Squad English OP
http://ca.youtube.com/watch?v=ot_Hx68kYzQ
I was made to hit in America. It's catchy. I was so surprised I actually liked this series, dubbed even.
Arashi no Naka de Kagayaite - Gundm 8th MS Team OP
http://ca.youtube.com/watch?v=rpWkTfS-cK4
The opening is funny and the song is nice
10 Years After - Gundm 8th MS Team ED
http://ca.youtube.com/watch?v=wxfK1jJHiAA
I like the way it was done, like someone was filming him and the main character is oblivious. I actually heard the song before I saw the series.
Rhythm Emotion - Gundam Wing OP2
http://ca.youtube.com/watch?v=VI4egy7qsfs
This will forever be one of my absolute favourite opening themes in the world. Forever I say.
That's probably way more than enough. ^_^