Ghost in the Shell: SAC_2045, on Netflix
A spin-off of Ghost in the Shell: Stand Alone Complex.

The Grimm Variations, on Netflix

The Melancholy of Haruhi-chan Suzumiya, on YouTube
A parody of The Melancholy of Haruhi Suzumiya.

Pacific Rim: The Black, on Netflix
A spin-off of Pacific Rim.

Pokemon Generations, on YouTube
An anthology series based on the Pokemon video games (not the TV series or movies).

Sailor Moon Crystal on Niconico (Japan) / Neon Alley and Hulu (USA)
ANN; Hulu; IMDb; TV Tropes; Wikia; Wikipedia

This 2014 original net animation is a reboot of the 1990s anime Sailor Moon, apparently based more closely on the manga than the old anime series was. (But I've never read the manga.) Anyway, I could watch this online, but first I want to rewatch the entire old anime series on Hulu, which I'm not sure when I might finish.

Scott Pilgrim Takes Off, on Netflix