One of my favorite 'go-to' websites is Freeology. This site provides a whole host of free, download-able graphic organizers (PDF's) that are easily adaptable to any lesson plan. Not only is the standard Venn Diagram available, but also KWLH, Fishbone, Spiderweb, Ladder, Chain/Sequence, Paragraph Hamburger, Open Mind, Vocabulary Exercises, Cause/Effect, and many more.
The website has a search bar, but I find it much easier (and quicker for some reason), to scroll down and zip through each page. When I find an organizer that I like, I click on the picture and save it to my computer. New stuff is added periodically. Here's one that's just been added:
