My top picks would be these in no order.
Pokemon
I really liked the first two seasons but then it kind of went downhill to me.
Yugioh
I enjoyed watching the original series though I couldn't get interested in the 5D followup.
Dragon Ball Z
As a young kid (about 10) the mindless violence of this anime offered countless hours of entertainment.
Sailor Moon
and finally the first anime I ever saw Sailor Moon I always appreciated the art style with this one ;)
Your turn feel free to list any of your favorites or laugh at my choices :)