I tried my best to put this in a specific order, but couldn't.
Great Teacher Onizuka, there are not so many anime that could make me laugh like this one, Onizuka was an amazing character. I wish he would have been my sensei.
One Piece, this is the dearest Shounen anime to my heart, though I like them all. I only stalled a bit while watching the series, maybe just two times, unlike in Bleach where I stopped watching the series many times especially after they just kill the adrenaline with fillers at inappropriate times. Speaking of fillers, whenever there is a filler in Naruto, I get disgusted. I know they are a bit better now at their fillers, but the amount of fillers in the original series made me bored of it. One Piece's fillers, on the other hand, are few and funny. If it wasn't for the massive amount fillers in Naruto and Bleach, they would have been on this list. I loved DBZ, it paved the way for other action and shounen anime, but it lacked something.
Hajime no Ippo(and it's sequel, OVA, and movie), I always love a story where the main character is a wimp that eventually becomes a tough guy. Hajime no Ippo is just that and much more. A lot of sports anime are addictive for me, in facts sports might be my favorite anime genre, but Hajime no Ippo has the comedy that many don't have.
Hikaru no Go, this is the anime that made me love Japan. It made me love it's culture and language. It also had an amazing soundtrack! HnG is the only anime where I loved and never skipped the openings and endings.
Eyeshield 21, on paper it may seem like Hajime no Ippo, but just a different sport. It has probably one of the greatest rivalries ever. Hilarious moments also add to its awesomeness.
Death Note, I think it is hard for anyone not to be able of noticing the wonder known as "Death Note". Every episode made me shiver in anxiety. I felt goosebumps down my spine and all over my body. It was an amazing thriller, a masterpiece.
Fullmetal Alchemist(and its sequel and movie), FMA was my introduction to the vast world of anime, even though I didnt know the term anime as I watched it. This anime made me admire Japan and East Asia in general. It is ironic, I used to make fun of my cousin for watching "cartoons" in "Chinese", though I have become much more of an addict to them than he will ever be.
Code Geass, a marvelous journey is what what watching Code Geass is. The thrill and the shockers, it is an unforgettable anime.
Black Butler(Kuro Shitsuji): This just made me amazed, I can't comment on how I felt.
D.gray-man: At first it was a bizzare anime to me, but I loved it and hated the fact that I finished it.
Honorable mentions: The Prince of Tennis, Slam Dunk, Whistle!, Beck, Psychic Academy, Hungry Heart - Wild Striker, Yu-Gi-Oh!: The Shadow Games, and Mobile Suit Gundam 00(and it's sequel).
