Albert Barnes Commentary Psalms 135:9

"Who sent signs and wonders into the midst of thee, O Egypt, Upon Pharaoh, and upon all his servants;" — Psalms 135:9 (ASV)

Who sent tokens and wonders - Tokens: that is, signs or evidences of the divine power. Wonders: things suited to impress the mind with awe; things outside of the ordinary course of events; things not produced by natural laws, but by the direct power of God. The allusion here is, of course, to the plagues of Egypt, as recorded in Exodus. See the notes at Psalms 105:27-36.