Unbiased: I would have to say, the most important Anime to date and the most influential is "Dragon Ball"
Biased: I Freaking Love "Full Metal Alchemist"
To a T Dragon Ball would be the most important, Laying the Ground lines for many Anime such as: "Naruto" and "Bleach"
Closely Following Dragonball Would be Pokemon, Now many people don't actually think of Pokemon as a actual Anime, However, it is, as childish as it may be.
In the third Spot I would Place Naruto
For being as Popular as it is Creative
In the Fourth Spot: Full Metal Alchemist
For its Interesting Plot and Deep Animation
Fifth I will Slide: Bleach
An Awesome Story with Intense Action