Our OT recomends "chewies", gum, and silly straws- the smaller the better. She actually prefers sugar gum because it is "chewier", although I rarely allow DS to chew it for obvious tooth-related reasons. DS' oral fixation has lessened considerably over the past year (he's 4 now).
My DS used to put everything in his mouth. I got him an electric toothbrush and he broke the vibrating part after using it twice. He has a chewy tube, but that seems too tiring for him to chew on much. He really liked his Sophie the Giraffe toy. Best of all, he likes crunchy foods. We also now do some exercises after he had a Beckman Oral Motor evaluation. They involve wearing a glove and praying you don't get bitten, but they do seem to help him with drooling, speech and chewing his food better (sensing where it is in his mouth). An OT will really help you come up with some good ideas for this type of stuff.
Re: On oral stimulation