If you can't find them fresh, frozen frog's legs are an acceptable substitute. It's quite lean, and if cooked correctly, it can be surprisingly good. Meat from older goats is tougher, like mutton. Mutton is cheaper than lamb, but it's tougher, fattier, and less delicately flavored. It's more popular in Europe than in the United States.
Ostrich looks and tastes like a cross between beef and chicken, and it's relatively low in fat.
Rheas are the South American version of ostriches. Rhea meat resembles ostrich meat, but it's even leaner.