Chickens and emus, although not often kept together, generally get along quite well if the chickens are raised with the emus, or introduced slowly.  If they aren't introduced right, the emus may see chickens as a threat and attack them. They shouldn't be kept in a small space together, as emus will often chase other animals, seemingly for fun, and the chickens should have someplace to escape to. 
Chickens and guineas (Numida meleagris) usually get along just fine, although there have been some reports of guinea males attacking roosters. Chickens and guineas will typically stay in two separate flocks, and may not interact much. Guineas are sometimes kept with chickens and other birds to act as a sort of 'alarm system', warning of predators with their loud calls.
Chickens and sheep typically get along very well, with each species generally ignoring the other. They are very often kept together. Chickens have been known to perch on top of sheep, and sometimes sit on them or even try to scratch through their wool. Lambs are sometimes curious about chickens and may try to chase or butt them, but this usually doesn't have any adverse affects, unless the chicken is cornered and the lamb will not relent.
Rabbits (Oryctolagus cuniculus) usually get along with chickens, provided that they ignore the chickens. If the rabbit(s) acknowledge the chicken(s') presence, however, the birds will usually become terrified. Rabbits are very curious, and may try to approach them. However if the chickens run away, they will often quickly lose interest.