Radak: In the heart.

'Rashi' (Divrei ha'Yamim I, 16:12): The plague of mice, and the cows who abandoned their young to take the Aron, and they sang (Shmuel I, 6:12), and the death of Uza. This entire Shir is about the Aron.

Gra (Divrei ha'Yamim I, 16:12): Pele is a new matter that was not yet in the world. "Ko Amar Hashem Tzevakos? Gam b'Einai Yipalei" (Zecharyah 8:6). Also refer to 105:5:3:2.

Malbim: They are one of three kinds of wonders not via natural means. Nifle'osav are like Keri'as Yam Suf, making the sun stand still, the manna? (people benefited from the miracle - PF). Also refer to 105:5:3:3, 105:5:4:2.

Radak: They are wonders that He did for Yisrael in Egypt, in the Midbar and when they entered the land, and the matter of the Aron in Eretz Pelishtim. For one miracle and wonder one is obligated to remember the previous wonders - "Zecher Asah l'Nifle'osav" (111:4).

Gra (Divrei ha'Yamim I, 16:12): Mofes is something found in the world, but it defies natural law.

Malbim: They are to clarify His words, e.g. turning the staff into a snake.

Radak: They are the Makos that He brought in Egypt via Moshe, who said before (each Makah). The judgments came on Egypt like he said with his mouth.

Malbim: They are Makos and punishments that He did in Egypt. It was a punishment for their sins via judgment. They were unlike all Mishpatim that He does in the world, for they were Mishpetei Fihu - He explicitly said with His mouth that He will do this Mishpat, and warned them before each Makeh. Also, He decreed beforehand "v'Gam Es ha'Goy Asher Ya'avodu Dan Anochi" (Bereishis 15:14).