Not everyone can write and edit. Since writing is all around us, text, text everywhere, we take it for granted. We think everyone knows how to write, knows how to edit, is sure that the stuff they've written is grammatically correct and makes sense and the words are spelled correctly. That's not always the case. Also don't overlook magazines and newsletters.
Many editors look for freelance or temporary help when it comes to editing or proofreading.
These are all great sites, not just for editing and proofreading, but for staff and freelance positions as well. Also, it doesn't hurt to pick up the phone and call a newspaper in your area to see if they need help. I know, I know. But let's face it, that's really where the steady money is. Besides, you'll make contacts you wouldn't have made if you were waiting tables or babysitting.