ok this is a ridiculously difficult question but I will try to answer it with some songs that haven't been mentioned:
1. Communication Breakdown (Xenosaga 2) - This is my first Kajiura track ever. Filled with emotion, great arrangement, electronica, strings, vocals.
2. Hikari no yukue (Hokuto no Ken) - My first Wakana song. People this is a pop song with Wakana but it has orchestra, epic Tokyo Konsei, composed of multiple parts, dead on brass AND beats. This is I think only one of examples where Kajiura really shines in combining pop and orchestra elements.
DO YOU KNOW HOW MANY PEOPLE HAVE NOT LISTENED TO "HOKUTO NO KEN OST" YET IN THIS FORUM ??? An OST I consider to be one of, if not the most, wholesome OSTs and one of Kajiura's best works.
3. Salva Nos (Fiction) - IMO the best Tokyo Konsei and Yuri combo resides in this song.
4. Total Eclipse (Tsubasa) - Kajiura's finest combo of rock/metal and strings and voila a most emotional track.
5. Hepatica (KOS-MOS) (Xenosaga III) - You think it's just Eri's beautiful voice and a calm melody for three minutes. and then... wonderful electronica and strings that add to the song so much.
6. Once upon a time there was you and me (Tsubasa) - Indistinct atmospheric chanty then wonderful flute/piano and then low strings.. strings take over, flute again.. then oops, the song changes tune so fast but so elegantly.
7. Endlessly (Tsubasa) - My first Eri song. She fits perfectly here. Tokyo Konsei plus wonderful melody and you have a song that refreshes you from top to bottom.
I described some of these songs in the Old Review Thread which I still haven't forgotten (..). :)
3. Decretum (Madoka Magica, also because I'm basic and Sayaka's "I'm stupid way too stupid" is the most iconic moment from the whole Madoka original series, fight me)
eh so true..