If you have all the expansions, then the only other things are the variants.
There are 4 commercial variant packs: the foil oversized villain pack, the oversized villain pack (which is redundant if you own the foils, but if you're really a completionist, they're a separate thing), the foil hero pack, and the complete hero variant pack (again, redundant if you own the foils).
Then there's the original promo variants. Here's where things get hard. They were mostly limited releases, and most are out of print. The original Young Legacy in particular is rare and worth quite a bit. But there's one of these for every variant, including villain variants. Argent Adept does have one weird one: the "original" is Kvothe Six-String and the "collector's edition" is the Dark Conductor.