According to wikipedia:
"Various mammals are omnivorous by nature such as bears; coatis; hedgehogs; opossums; pigs; some primates including chimpanzees and humans; raccoons; some rodents including chipmunks, mice, rats, and squirrels; skunks; sloths.
Various birds whose diet varies from berries and nectar to insects, worms, fish, small rodents, and snakes — cassowarys; chickens; corvids including crows, magpies, ravens, and rooks; keas; rallidae; rheas.
Some fish such as piranhas.
Some insects and other invertebrates are also omnivores."