Well my vote went to Bleach. But it's closely followed by Naruto and after that it's Inuyasha, Death Note, Ouran High School Host Club, and Pokemon since Pokemon defined my childhood. I've always wanted to start watching FMA but never really got into it...
It's a small list.
"I think the world is just going through a phase...It'll pass, maybe not for a hundred years but someday...I still believe, inspite of everything, that people are really good at heart." -- Anneliese Frank
My top 5 is for sure. The rest that follow change places with each other...whichever is 10 might get swapped with another series from time to time:
1. Gunslinger Girl 2. The Melancholy of Haruhi Suzumiya 3. Kino's Journey 4. Tengen Toppa Gurren Lagann 5. Eden of the East 6. Samurai Champloo 7. Darker Than Black 8. Neon Genesis Evangelion 9. Last Exile 10. Sayonara Zetsubou Sensei
Honorable mentions: K-On!, Full-Metal Panic, Durarara, and True Tears