Personally, I think the ASPCA and Humane Society don't need donations. Or any more than they already get. They're big "companies", people always know about them.
It's the little, private community ones that are suffering. The one I volunteer at is hundreds of dollars in debt with vet bills, we're always struggling to get decent food (the stuff people donate is the cheap grocery store stuff that only makes the cats sick with vomit and diarrhea all the time).
I like the fact that we're no kill...but we now have over 200 cats in our program, and we keep taking more! I keep telling the supervisor that we need to start saying no to new rescues...it's hard, yes, but now the other kitties are starting to suffer for it, because we just don't have the funds to care properly for that many >_<
Plus, the shelter is getting crowded. We don't have cages, so the cats are out and about...which I guess makes it seem like there's more room. But it's getting so that the cats are starting to fight daily, as there's really not enough room for little personal territories and cats are getting in each other's "personal bubbles" even just to lounge around, let alone crowd around the food and water bowls.
Petco and/or Petsmart usually works with smaller, local groups. Ask there for some ideas.