Any non-legendary? Screw that. If your Beldum is an Adamant nature, I'll offer you a Ho-oh, Lugia or a Deoxys (Mew I could do, but I'm rather attached to that bugger).
Each are legit, far as I know. Traded from a few friends on Emerald, and caught at those Islands. Maybe someone used the warp cheat, but I guess they'd still technically be legit.