There are way too many Collectibles for AC, especially the rare. There are lots of rare Items that I don't have. but in my opinion I can consider it as the best already.
Here's my top Best AC collectibles. some of them I don't have it. but hopefully one day I can find one.
1) ACII Ezio Hidden Blade replica
2) AC2 italian Press Kit
3) Revelations by Craig Mullins
4) Tomahawk Statue
5) Crouching Altair
6) Unpainted Statues
Spoiler!
I know some of you will not agree with me, I like collecting statue but I find unpainted statue a beautiful piece, very unique and rare. first time I see unpainted is AC2 Ezio from white/black edition and I keen for one. so when they announced this unpainted edward, I need to get this and I bought one.
I know unpainted statues are like incomplete products, but the way I see it. they are rare and very unique for display

7) Duomo di Firenze
8) Edward Kenway Pistols,
9) Codex book (Promotional)
10) Desmond Outfit
Well, this is in my opinion, the BEST Collectibles for Assassin's Creed.
That being said, there are LOTS of collectibles out there. I might not know few of it.
Now, I want to know what's others opinion and let's agree upon it