In no order.
1) Nobuo Uematsu (Final Fantasy) - A man whose body of work needs no explanation or introduction. He's composed some of the most recognizable themes in the history of video games. Even his less memorable work (FFVIII in my opinion), remains incredibly nuanced.
2) Yoko Shimomura (Parasite Eve, Kingdom Hearts) - A woman of variety, maybe not as much as the other "Yoko" in the composition field, but responsible for some incredible soundtracks. As much as I loved Super Mario RPG, Legend of Mana and Kingdom Hearts, I gotta give it up for Parasite Eve, which is definitely my favorite of her discography. Here's hoping she returns for 3rd Birthday.
3) Yasunori Mitsuda (Xenogears, Chrono Cross) - Responsible for Xenogears and Chrono Cross, either of which alone would cement his place on any list like this, but then you factor in Chrono Trigger and Soma Bringer, not to mention the arrange albums for Trigger and Cross and it's not difficult to see why he's revered as much as he is.
4) Shoji Meguro (Shin Megami Tensei) - A man of eclectic composition capabilities. Campy, retro, modern, heavy hitting seemingly all at once with his own personal blend of rock and j-pop. I haven't heard his entire body of work, but I've definitely heard enough to say he deserves to be mentioned. One of my favorite composers ever, I feel cooler just listening to his work.
5) Yoshitaka Hirota (Shadow Hearts) - Another man with a very distinct style. I love his blend of ethnic industrial which seems to be unique to Shadow Hearts. His library of compositions is sadly not as large as it deserves to be, and with Shadow Hearts kaput, I'm not sure where he's headed. Tragic, but the four Shadow Hearts albums we got were amazingly good, so much so that I think he deserves a spot.
6) Miki Higashino (Suikoden) - The lighter side of ethnic influenced composition that I've grown to love in recent years. Her style is punctuated with harmonious leads and ethnic hooks of various styles, to my ears it's a good sound, and one of the rare instances that I call inconsistency a good thing. She's worked on other stuff, mainly a bunch of shmups, but the biggest surprise is that she worked on Moon Remix RPG Adventure, which I'm still dying to play.
7) Hitoshi Sakimoto (Vagrant Story, FFXII) - It is difficult for me to explain why I love this man's work. He is capable of composing sweeping, epic songs, fluent with energy just as easily as he can produce songs of quieting introspection. His work on Vagrant Story is by and large my favorite for it's dark tone and creeping, rustic composition. I loved the man's work on Odin Sphere and am currently in love with Muramasa: The Demon Blade
8) Noriyuki Iwadare (Lunar, Grandia) - Upon reflection, I'd say that Iwadare's style leans closer to the traditional conception of RPG music, that is, what I imagine when I think of the genre's earlier trappings. His work on Grandia and Lunar was perpetually sunny and upbeat and his later work on Langrisser was a delicious treat. His whole style reminds me of glam rock in that it's cheesy and not really nourishing, but wholly enjoyable.
9) Hiroki Kikuta (Secret of Mana, Soukaigi) - Let's forget the massive boat of fail that was Koudelka in it's entirety and remember that at this man's peak, he did some of the most classic VGM of all time. Secret of Mana, Seiken Densetsu 3 and Soukaigi are some of the most iconic works of VGM available and to not mention this man in a list like this seems a horrible disservice.
10) Michiko Naruke (Wild Arms) - In all honesty, I haven't heard every Wild Arms soundtrack completely, but what I have heard, I've loved. Her work on the series combines traditional RPG composition with instrumentation that is strongly redolent of the old west to create a style that is unmistakably hers. I look forward to playing through the actual games to complement what I've heard.