Why Frogs?

Of all the things that Hashem could punish the Egyptians with, why would he choose frogs?  
Here are a few reasons given by the classical commentaries:

1. Rashi cites a midrash that the plague of frogs began with one giant frog emerging from the Nile.  The Egyptians ran out to kill it, but as they hit it, the giant frog multiplied.  This could have been to teach the Egyptians and all those who came after to oppress the Jews that the more they oppress the Jews, the stronger they will become.
2. Saadya Gaon suggests that the frogs were actually crocodiles.  Presumably because the Egyptians worshipped crocodiles and Hashem was demonstrating that He was in control of everything.
3. Midrash Rabbah: because the Egyptians would afflict the Jews with gratuitous repulsive tasks such as making them fetch slimy creatures.
4. Lekach Tov says that the Egyptians would come into the Jews' houses at all hours of the night and scream at them to get out of bed and get to work.  The frogs did that to the Egyptians.
5. The Zohar says that the Bnei Yisrael are the nation that calls out to Hashem at all times of the day in prayer.  So Hashem brought the creatures that also call out at all times of day.
6. Similarly, the Siftei Kohen says that it was punishment because the Egyptians prevented the Jews from reciting Shma in the morning and in the evening.
7. The Siftei Kohen also says that the Egyptians made the Jews eat their bread with slimy hands.  The frogs jumped into bread and punished them for that.
8. The Abravanel says that the screaming croaks of the frogs coming form the Nile river were meant to haunt the Egyptians as if the screams of the murdered children were coming from the Nile.
9. The Me'Am Loez says that during the decree to throw children into the Nile Jewish women gave birth in hiding and were forced to hold in their screams which caused them extra pain.  The screaming of the frogs was punishment for that.
10. Rav Shimshon Rephael Hirsh says the frog represents a lowly creature which usually runs from man.  During the plague the frogs hopped all over the Egyptians with impunity teaching them, "how even the lowers and smallest of animals had lost all respect for them, in order to heal them from their overbearing arrogance."

(answers 4,5,6, and 7 were found in Sharei Aharon.  Great sefer, I highly recommend it.)