Dragonball Z and Pokemon paved the way when I was younger. However, I really got into anime after watching Elfen Lied, FLCL, FMA, and Cowboy Bebop. Also, Elfen Lied got me to read manga.
DBZ, Gundam Wing, Tenchi Muyo!, Sailor Moon, Yu Yu Hakusho, Naruto. Basically anything Toonami had aired over the years but DBZ Gundam and Naruto were the big ones.
I'd say pokémon, but it didn't really get me into it, I just watched it as a kid.
Code Geass and Full Metal Alchemist were two of the first few that I watched whilst getting into it. I was watching a few at a time so there wasn't really one specifically.