I have a sweetgum tree, so I have lots and lots of sweetgum "balls" every year. I put them around the garden and sometimes particular plants to keep slugs away. If you aren't familiar with sweetgum fruits, they are about the size of golf balls, but covered in sharp spines. I have also used them to keep wandering cats from using flower beds as litter boxes. It is easier to dig somewhere else. They might keep squirrels from digging up bulbs, too.
Before I got a bird bath, I used to have trouble with squirrels taking the occasional green tomato or unripe squash to quench their thirst during dry spells. A bowl of water on the ground is supposed to deter this, too.
Of course, the water needs to be changed frequently to prevent mosquito problems (and West Nile, St. Louis encephalitis, etc.)
I have a chicken wire fence around my little veggie garden and I don't seem to have rabbit or mouse problems. I have heard that putting cat hair around your garden will help keep fury pests away though.
I have Japanese beetles here that attack my roses, raspberries, and cherry bushes. I have heard that Japanese beetle traps actually attract more of them to your yard. (They use a pheromone in the traps to attract them.) I had read a hint once about knocking the beetles off of branches into a bucket of dilute Murphy's Oil soap and water. They fall before they start flying. I use hot water, just to make sure. I splash a cool bucket of the Murphy's Oil soap solution onto the plants, too.
I guess those are about all the hints I have. Does anyone else have some to share?