Exactly as FJames said.
If you are after a specific one, I use the Genuine Apple i-products (iphones/ipods etc) chargers to great success. These have a 5V/1A output which works great - providing more current than required, and I just happen to have a handy collection of them about. Also great if travelling as it meets spec for both my phone (iphone) and eReader (Kobo Touch) so I don't need to take multiple, just the two cables.
Edit: ldrover beat me to it