As far as linking this site, we are link-free! If you want me to provide a link to your site if you have anything Hanamori Pink or Nakayosi related please e-mail me! dream@my-will.org. I currently don't have any buttons to provide for you, but a text-link would be fine or if you want to make one yourself, that would also be good.
Official Sites
LIPS; Hanamori Pink's very own Official Site. Her current splash page features Yume, and hopefully she'll have some different drawings for Y*Y here. -- but there's illustrations from PPP and more.
Nakayosi; Especially since Y*Y is currently running, you can preview furoku from volume to volume as well as find out any news about any other releases from Hanamori Pink.
Yume Yume * You You Fansites
None currently that I know of. If you have a site or shrine dedicated to one of the characters or even have a site dedicated to the series, let me know and I'll add it here!
Other
Pearl Song My favourite & best site for Pichi Pichi Pitch -- which is another one of Pink's works, and has also been my favourite manga series for a couple years now. There is everything from chapter translations, to amazing character profiles.