I read manga off and on (have read quite a few, and mostly not stuff that's mainstream here in the US), too many to list. As for webcomics... currently:
My current list of webcomics I am following consists of:
Saturday Morning Breakfast Cereal (SMBC)
Questionable Content (QC)
Least I Could Do (LICD)
Too Much Information (TMI)
Simply Sarah
Yet Another Fantasy Gamer Comic (YAFGC)
OGLAF
Between Failures
Nerf This
Girls with Slingshots
Snafu.com - Grim Tales, Sugar Bits, Powerpuff Girls (3 comics by Bleedman)
Yaoi 911 "Artifice"
The Other Grey Meat (TOGM)
Avengelyne
It looks like a lot but only about three update daily, the rest can vary from one a week to once a month.
A few could be classified as graphic novels but the rests are comics and works in progress in terms of art style. I've found the better the artwork the less original the content when it's posted only online.