Sleazy Fork is available in English.
Can work on almost any webcomic/manga page, preloads 5 or more pages ahead (or behind), navigates via ajax for instant-page-change, lets you use the keyboard, remembers your progress, and it's relatively easy to add new sites
Doesn't seem to be working on SmackJeeves right now since they changed the site, anyone know the site settings I should use to fix this?