If you liked
Digimon Tamers
|
...then you might like
Mahou Shoujo Madoka★Magica
|
Both series begin as your usual magical girl/mon show and flip the genre completely, getting progressively darker with themes and elements completely unexpected of the childrens show they initially appear to be.
If you liked
One Piece
|
...then you might like
Fairy Tail
|
First off, both are based on long shounen manga series, so they follow a bunch of story arcs in addition to the main goal. The artstyles are quite similar, with characters looking very lanky and lots of wild and colorful animations. Both also have a general theme of friends/teamwork/nakama, with the main teams of the series (Team Natsu for Fairy Tail, Strawhats for One Piece) always working with and fighting for eachother.
If you liked
Witch Hunter Robin
|
...then you might like
Darker than Black: Kuro no Keiyakusha
|
Both revolve around a small group of people with certain abilities and follow a "case of the week" sort of pace until the end where they both break into their main story arcs dealing with the mysterious pasts of the protagonists.