Capcom Fighters:
Ken, Sakura, Dan, Remy, Vega (Claw), and Makoto from Street Fighter
Jon Talbain and Felicia from Darkstalkers
Tessa and Leo from Red Earth
Ingrid from Capcom Fighting Jam (somehow)

SNK Fighters:
Iori, Ralf, K', Geese, Athena, Leona, Yuri, and Shermie from King of Fighters
Amakusa, Mizuki, Galford and Rera from Samurai Shodown
Setsuna from The Last Blade
Yuki from Neo Geo Battle Colosseum

Other Fighters:
Testament, Baiken and I-No from Guilty Gear
Raiden, Liu-Kang, Kitana, and Shang Tsung from Mortal Kombat
Warakia from Melty Blood
Senna and Agito from Big Bang Beat
Shimo from Yatagarasu
Jimmy and Annie from Rage of the Dragons
Keith Wayne from Power Instinct
Celia II from Chaos Code

I might be forgetting a few characters, and this isn't counting a sh!tton of edited Mugen creations.