I did want to create a list of some of my favorites at some point, but this format seems easier without the constant need to edit the first post with new stuff and I don't have to spend an hour or more finding and deciding which are my favorites.   Of course, I won't mind if other people post their own picks.  I know only one or two people will probably follow this thread however...

Since I couldn't decide which one I wanted to give the first day's spot to, I'm compromising and posting both.  And this has been another rendition of "Seki still can't create a thread that doesn't look like garbage"

Probably my favorite by a small margin, if for nothing else the subject matter:  Mecha or the closest thing Touhou has to mecha.   I love everything about this animation.  It has: my favorite vocal rendition of "Our HisouTensoku" (which sounds straight out of the opening of an 70's/80's mecha anime), quality animation for a fanwork (especially movement imo), a fight between Mazinger Z and Big Zam expies, and (probably) a funny look into Sanae's imagination. Plus Yukkuri=Reimu missiles          Marisa as a reluctant sidekick and labcoat Okuu only seal the deal

Second is this animation.  I don't know the name of the song, but it always went well the animation (featuring the casts of Touhou 6-12).  A lighthearted piece overall that is fairly nostalgic now, since I first saw this back when it was released in 2010.  

Edit:

Found a subbed version of the second

緋色月下、狂咲ノ絶　-1st Anniversary Remix-