Oh, wow, there are just so many...
Okay, better choose carefully... (Sorry, but I'm probably going to spell EVERY one of these wrong -_-;)
[In no particlar order]
Gundam Wing - "Rythym Emotion Pure," "Just Communication, 2nd Variation," "Endless Love," "Burning Love," "[uhhhh.... will NOT get this right....]Sandy Clock of a .... somethin'

[I'll have to dig this one out]" (sounds best in piano, a super awesome 9min mix, a few seriously cool songs, and a super sad theme with a name I could never find the REAL name too -_-; I'm probably the only one that enjoys the music overall-- minus the image songs >.<) Two Mix. Mind Generation.
GW: Endless Waltz - "White Reflection," "Last Impression," and "Snow Planet" (Yup, even this has a remix) Two Mix. Mind Generation.
Bubblegum Crisis Tokyo 2040 - "Y'Know" and "Waiting for You" (because they're ... rock opening/ending... such coolness)
Inuyasha - "My Will" and "Fukai Mori." "Shippo's theme," Sango's theme, and any of the Kag/Inu themes (I Love all of the endings. But those were my first two favorites, duh ^^ Has a VERY good soundtrack.) Kaoru Wada
Escaflowne - "Hikari no naka e [Into the Light]", "Arcadia," "Shadow of Doubt," and also.... "Ask the Owl" (the 2nd is actually... an operatic song, but wow, one of my favorite songs ever. the3rd a cello duet. that last one centers around......clocks ^^ Kanno-sama can do anything

3+ soundtrack anime... I'll never get enough of it) Yoko Kanno.
Escaflowne(Girl in Gaia) - "Sora" (a spell/chant. so beautiful...) Yoko Kanno.
Fushigi Yugi - "Itooshi Hiten no Tame ni [For My Loved One]" (The opening song is awesome)
Rahxephon - "Hemishere" (so awesome. a symphony in itself. yet another Maaya Sakamoto/Y.K. opening) Yoko Kanno.
Outlaw Star - "Hiru no Tsuki" and "Tsuki no Ie" (these op/end themes are to be my "fav")
Blood Reign: Curse of the Undead Yoma - "[Yoma counting song]" (it's evil... it's counting.... oh yeah)
Twelve Kingdoms - ending (I have such a bad memory for names... but it's a very good song... a "keep going" song)
Cowboy Bebop - "Jupiter Jazz," "Blue," "Real Folk Blues," and "Mushroom Samba" (a sultry saxaphone, a deeper shade of blue, a broken heart, and childlike innocense..... a truly eclectic soundtrack) Yoko Kanno.
Serial Experiments Lain - "Duvet"** (just... so.... UGH.... meaning, good

) Boa
.Hack//Sign - "In the Land of Twlight, Under the Moon" (a haunting soundtrack with a seemless blend of voice/ instrumentation that few know of. very full of emotion.) Yuki Kajura.
Laputa: Castle in the Sky - end/theme (my mom's watching it downstairs... so pretty.... one of the prettiest songs from a Hayao Miyazaki)
Samurai 7 - "Fuhen"* and preview (the endsong is sad. the preview.... like "shippo's theme" revised

) Kaoru Wada.
Ghost in the Shell (movie) - "Reincarnation" (beautiful, haunting)
Scrapped Princess - ending (purdy... neat duet)
MS Gundam: 8th MS Team - op and "Ten Years After" (cute op/ending themes)
Planetes - op/end (they're VERY hopeful.... a true rarity to hear something that inspires)
Neon Genesis Evangelion - "Cruel Angel Thesis" (one of the most popular/cult fav openings) "Fly Me to the Moon" (a sinatra song *heh* my mom loved hearing a different version of "Fry" every ep or so)
Ghost in the Shell S.A.C - "Inner Universe" (like, only THE coolest opening ev-ah!!) Yoko Kanno.
*YAWWWWN*
That's all I can think of for now. (Will probably add more later.... maybe... *falls asleep*)
EDITS: (yes, I'm SO forgettful... -_-;)
(*)Fuhen is part of a title of a story arc I wrote. It means lots of things... but I chose "eternal."
**"Duvet" has memorable english lyrics... "I am falling, I am fading... I am drowning..."