None. It finishes just before you start your turn, and you can act normally on your turn.Joker said:If I start casting a summon Monster spell during the surpise round, what kind of action do I have to take next round to finish the spell? Move or Standard?
OK, I'm an idiot. I completely did not see the word "suprise".isoChron said:Not quite right.
In a surprise round you can only take a standard action.
In this case the standard action is starting a full round action.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.