D/P - Advance - Hybrid - Platinum
You may direct link sprites from this page if you have to, but if you're planning to use them on your site or something you should really just upload them yourself.
Unown and Arceus can take a while to be generated, thanks to all their different forms. Just be patient.
For Nidoran, enter "Nidoranm" or "Nidoranf". Entering a Pokémon that has multiple forms will show all of them.