strictly in terms of series that I revisit rather than impactful stuff that I don't ever realyl reread?
longer ones:
hitori bocchi
girl's und panzer ribbon warrior
normal length stuff you can easily swallow in a single session:
mimi mix!
The Real Her
Pink Ribbon
Pink Rush
The Tiles that I cannot Cut are next to None
Seifuku no Vampiress Lord
Spectral Wizard