Here's a few Goosebumps books to help jog your memory:
Say Cheese and Die
This one was about a bunch of kids who find a camera in an abandoned house that is said to be haunted by a mad scientist. When bad things start happening to anyone snapped in the pictures, the lead character Greg begins to suspect that there is something sinister about the camera.
This was actually the first Goosebumps book that I read. It was basically about a kid (Evan Ross) and his friend finding a can of novelty "slime" in his aunt's house. It consumes everything in its path and even turns his dog into a giant.
The Barking Ghost
The Barking Ghost was about two young boys who are stalked by two stray dogs and tricked into trading bodies with them. I think this was actually the last Goosebumps book that I read.