Also here are some cards that are probably not going to make the cut but cool interactions nonetheless:
Finale of Promise - since two replacement effects take place you choose which to apply. For any amount of
X you cast two spells from your graveyard and instead of exiling them they'll return to your hand. If
X is 10 or more you'll cast both spells three times and they'll return to your hand. Or at least I'm pretty sure how that works.
Grapeshot - if you target the original copy to Feather you'll get to keep the card and use the copies for other targets. Under normal circumstances with no other interaction and stock Feather (toughness 4) you can do this three times. First time targets Feather, resolves. Second time has a single leftover copy and the original still targets Feather. Third time you'll get two copies and the original still targets Feather. Ok, it's elaborate but it gets exponentially more powerful for each spell you cast before it and you always get it back.
Astral Steel - same logic but it just pumps Feather a lot. Sadly the +1/+2 isn't nearly as powerful as it could be.