Format stolen from iindigo
One favorite song? Well, I don't think I could choose just one, but here's a few in my favorites list:
• Girls Can Rock and Feel Like A Girl from School Rumble Insert - These were both sung in the same episode, and were overall very fun to listen to. Sung in accented English, although in the show, the character (and her seiyuu) are Japanese, it's actually sung by someone called 'Lia', who I assume, does not have Japanese as her first language.
• Scramble from School Rumble OP - When I first heard this, I thought the song so embodied the boundless energy of the main character, Tenma, and thought her seiyuu had sung this because it was so energetic and slightly different, wiht a full band behind it (including saxaphones!). I later found out that it had been sung by Horie Yui, the seiyuu for one of the other main characters, but nonetheless, that impression of endless energy carried through and this is a track I continue to listen to.
• Dramatic from Honey and Clover I OP - Sung by YUKI, her distinctive voice matched the overall mood of the series and the way the music was structured, fit the OP visuals. Fun to watch, excellent to listen to.
• Suki Dakara from Bokura Ga Ita Insert - The series was a bit sappy and some say emo, but this song, played during Yano and Nanami's first big moment was very powerful. The song was so ... calm and it really gave the scene emotional impact.
• 1000% Sparking from Negima!? OP - This track has such energy, and if you've seen the performance at the Princess Festival (on Youtube) you'll know what I mean. It's structured to use voice clips from the episodes, and allows the seiyuu to sing. Not only that, but because of that speaking/singing format, they were able to include a huge number of the female seiyuu into the performance and stretch this track to over 15 minutes, without it getting boring (for me at least). The CD version is only 4:23 long, so no worries.
• Bouken Desho Desho? from the Melancholy of Suzumiya Haruhi OP - I use this to wake me up in the morning (as part of an alarm program). The bells at the beginning behind the vocals seem to signify ... hope, or something. It's a beautiful track and currently at the top of my Last.fm. If we were talking Character CDs, I'd be adding quite a few tracks, but we're not, so I'll just give them an honourable mention. Never have I felt the Character CDs captured so well, the personalities of the characters.
• Futari no Kisetsu ga from Bokura Ga Ita ED - Sung by Sasaki Nozomi (the main female character's seiyuu) and enjoyable to me because I think Sasaki Nozomi has one of the best moe voices out there. It's not annoying, and in a forlorn song like this, it's very effective.
• Keikenchi Joushouchuu from Minami-ke OP - Full of energy (do you see a theme), sung by the three main seiyuu (one of which, is Chihara Minori, an excellent vocalist), and full of chibi-voicings, this song is best enjoyed first by watching the Minami-ke OP sequence. Ayu has done a great job subbing the karaoke and I believe they captured the chibi-phrases very well, and has made this song enjoyable even when I'm not watching the OP sequence. Also, the key they chose to move into from the chorus into the verse held up the excitement/tension, which of course, kept up the energy. Another 'good morning' song.
• Morning Grace and Watakushi no Koi wa chiisai keredo from Princess Tutu OP/ED - To be honest, I'd include the entire OST because, even though most of it is Classical music, quite a bit of it has been adapted to the scenes of the show, and their use of it was absolutely beautiful. Speaking about the OP/ED though, both were written and performed by Okazaki Ritsuko and are absolutely stunning. Both incorporate classical music (I think both use selections from Tchaikovsky's Nutcracker Suite) and Okazaki did this seamlessly. I'm not even sure what to say about them except that after viewing the OP, I had very high hopes for the show, and afterwards, watching the ED, was thinking that it was a very tasty cherry on top of a exquisite cake.
• perfect blue from Dragonaut OP - Unorthodox beginning, and sound effects that made you feel like you wanted to move with the music as it zoomed around. It's hard to put into words, but I think this track is almost too good for the Dragonaut series, which suffers from a couple weak characters and a sometimes iffy storyline, whereas this track is flawless. And yes, this one wakes me up in the morning too.
• Prism from Dennou Coil OP - It instantly makes you wonder what's about to happen. The mood this song evokes from me is one of curiousity, and I feel this suits the Dennou Coil storyline (particularly at the beginning of the series) to a T. The selection of synthesized sounds was very, very good.
• Reflectia from true tears OP - The string introduction almost makes you feel like you've stepped back into the Classical period, but the vocals swoop in with the 'percussion' and 'tinkling', and you're left with a sense of wonderment. The light use of instrumentals, with only a bit of piano responding to the voice, allows the listener to focus solely on the melody, which leads into some colour chords, and consequently to the key change (actually, an unstable section where it moves through several keys quickly) and into the chorus. The instrumentals in this song had such an intriguing dialogue with the vocals that is so rarely seen in pop music. Kikuchi Hajime, [a.k.a. cuckool, half of eufonius, (the other half being riya)] also wrote/arranged CLANNAD and Futakoi OPs (riya also providing vocals for those), appears to draw on Classical music writing techniques, which is a great, great thing.
That ended up taking longer than I expected. I left out some others that I thought people wouldn't be so interested in.
Dishonourable Mention: Code Geass: Never have I enjoyed a series so much, with OP/EDs that I've disliked so strongly.
Honourable Mention: Sasaki Yuko - Pure Snow: If anyone has a source for a HQ audio of this, I would love it. Attached to a mediocre show (Himiko Den), it uses the timbre of strings to full effect and written in DM/FM, it's just a wonderful song (lyrics glorifying romantic suicide notwithstanding)