have you read the other mspaintadventures stories? Hetalia is history comedy and manga combined but sadly. it is a manga and not the flash, interactive style like homestuck. whenever i think of web comics the first thing that comes to my mind is the shipping of Andrew Hussie and Himaruya :D
Yuumei's stuff is pretty good. There's Fisheye Placebo, which is being updated pretty regularly recently. Then there's Knite, which I think was put on a hiatus for the time being so she could focus on Fisheye Placebo.
Oooh webcomics are my thing. The Property of Hate, any of the Overside comics (Rice Boy, Vattu, Order of Tales), Badirfilay , Nimona, and Prague Race are all I can think of right now. Prague Race is my favourite at the moment, and Todd Allison and The Petunia Violet is also worth a read.