Is there a PSPACE-intermediate language?
This is corollary 13 in Uwe Schöning's paper "A uniform approach to obtain diagonal sets in complexity classes":


  Corollary 13:
  
  If $\mathsf{PSpace} \neq \mathsf{PH}$, then there exist sets in $\mathsf{PSpace}$ which are not $\mathsf{PSpace\text{-}complete}$ w.r.t. $\leq^{\mathsf{P}}_T$ and which are not in the polynomial hierarchy.
  
  Proof:
  
  If $\mathsf{PSpace} \neq \mathsf{PH}$, then QBF is not in the polynomial hierarchy.
  Hence $A_1 = \emptyset$, $A_2 = QBF$, $C_1 = \{\mathsf{NP\text{-}complete} \text{ w.r.t. } \leq^{\mathsf{P}}_T \}$, $C_2 = \mathsf{PH}$, satisfy the hypothesis of the main theorem. 





  Main theorem:
  
  Let $A_1$, $A_2$ be recursive sets and $C_1$, $C_2$ be classes of recursive sets with the following properties:
  
  
  $A_1 \notin C_1$, $A_2 \notin C_2$
  $C_1$ and $C_2$ are recursively presentable, 
  $C_1$ and $C_2$ are closed under finite variations. 
  
  
  Then there exists a recursive set $A$ such that:
  
  
  $A \notin C_1$, $A \notin C_2$, 
  if $A_1 \in \mathsf{P}$ and $A_2\notin \{ \emptyset, \Sigma^* \}$, then $A \leq^{\mathsf{P}}_m A_2$. 
  


(note: I updated the names to current ones)



There are two interpretations for monotone QBF:


QBFs where the quantifier free part is monotone in all variables. Then this is in $\mathsf{P}$ as Ryan noted. Because the quantifier-free part is monotone in quantified variables we can remove the quantifiers and replace the existentially quantified variables with 1 and universally quantified variables with 0, the original quantified formula is true iff this modified quantifier-free formula is true, and this reduces the problem to monotone formula evaluation which is in (and complete for) $\mathsf{NC^1} \subseteq \mathsf{P}$. (If we are taking supremum of a function over a variable and the function is monotone in that variable we only need to compute the value of the function over the maximal values for that variable.)
QBFs which are monotone in the input variables. This is $\mathsf{PSpace}$ under $\mathsf{AC^0}$ reductions, the reduction of the QBF to this version is simple and is similar to the proof for monotone boolean formula evaluation being complete for $\mathsf{NC^1}$ or monotone circuit value being complete for $\mathsf{P}$.