Spoiler season officially starts tomorrow! I'm still excited, even though I don't particularly love most of the cards spoiled so far.
Runeforge Champion might be interesting, depending on how cubeable Runes are.
Sigrid is really, really sweet as a surprise blocker to potentially 2-for-1 someone, though the body is small enough for her not to be obnoxious, I feel.
Dragonkin Berserker is a solid token maker, but it might be too much if a removal check, as the token making feeds in on itself, and it doesn't take much for it to get out of hand and become "
: Create a 5/5 flyer"... The one per turn clause might keep its power level in the right power band for my cube though.
After those few we have to go all the way back to the first few cards spoiled...
Rampage of the Valkyries is a really interesting Serra Angel variant to me. It might be too expensive at 3WB (not for the effect, but in general), but I do have a small Angel theme going on, so who knows?
Showdown of the Skalds is a super interesting curve topper for Boros aggro decks. It's a saga, which triggers the historic cards, a mini archetype in white, its card advantage in a color that's in dire need of some, and it still gives you board presence if you can keep some creatures alive from t1-3. It looks awesome!
Fliplands. We already know them from Zendikar 3 (4?), but thsee are incredibly versatile, and the fact that they enter untapped is huuuge!