This poll is highly deficient in choices, only listing three shounen series... I certainly don't mind naruto, but it's nowhere near the best anime. Entertaining though, certainly.
Anyways, of the many, many series I've watched all or parts of in the past 15 years, this would be my top list....
Ranma 1/2
Death Note
The Melancholy of Haruhi Suzimiya (except for that endless 8 nonsense)
Code Geass
Neon Genesis Evangelion
Clannad/Clannad After Story (well, except for the ending)
Sayonara Zetsubou Sensei and sequels
Love Hina
.Hack//Sign
Eden of the East
Azumanga Daioh
Excel Saga
Toradora
Maison Ikkoku
Hikaru no Go
Fushigi Yuugi
Noir (if we pretend the last 2 eps never happened...)
Mai Hime
Kimi ga Nozomu Eien
Welcome to the NHK!
Rurouni Kenshin
Yakitate! Japan
Patlabor
Oh My Goddess!
Card Captor Sakura (original Jpn version)
Ayashi no Ceres
Angelic Layer
Genshiken
Full Moon wo Sagashite