This would be an excellent choice for wildlife and under $500 used. Make sure to get the VR version.
Gobuster wrote:
Since you already have an 18-55, you might consider the Nikon 70-300 F4.5-5.6 VR it's sharp, also works on FX format and is under $600 at Adorama. I have one and like it a lot, used on both DX and FX body cameras.