Fanaelialae
Legend
Oh! If Haste is a separate spell effect someone cast on you? Yes, then Haste would still apply. I thought you just meant, like, the Monk's "I'm extra fast" thing. Which would not apply polymorphed...nor would some magic item making you hasted last. But a separate/independent spell effect, yes, that would still be working.
Not one cast by the Monk on themselves (as in the case of a Monk/Sorc or some MC nonsense like that)! Once polymorphed, anything the MONK was doing/could do is gonzo.
I could see that if the spell is concentration based (since it's not entirely clear whether a beast is capable of concentration) but not for independent effects such as Mirror Image. I would rule that those remain, since they're not dependent on the caster.
Similarly for items. I think a potion would still work, even if you consumed it before being polymorphed. On the other hand, a Hat of Disguise would cease to function because it's arguably removed when you absorb it. Similarly, a Mantle of Spell Resistance would also cease to function, since you're no longer wearing it. However, if you used a Mace of Terror to frighten creatures before being polymorphed, I would say that they remain frightened even after polymorph. As a rule of thumb, I would say that if you can drop the item and have it continue to function (or cannot drop the item, as in the case of a potion) then it would continue to function even after you are polymorphed.