Determine number of values less than mean in one pass through list
Consider an algorithm for arrays of length $n$ consisting of entries from $0$ to $n$, and using space $S$ bits.

Suppose that the first half of the array consists of pairs $a,n-a$ (where $a \leq n/2$). By choosing the second half appropriately, we can make the average of the entire array anything from $n/4$ to $3n/4$ (discretized to multiples of $1/n$). In particular, the state of the memory after reading the first half should store the number of pairs with $n/4 \leq a \leq n/2$. For every non-empty subset of $\{n/4,\ldots,n/2\}$, we can construct a first half of the array which contains exactly these values of $a$. This shows that the number of first halves that are pairwise distinguishable is at least $2^{n/4}$, hence $S = \Omega(n)$.

A very similar construction establishes an $\Omega(n)$ lower bound even when replacing the mean with the median.