"Let us build a city and a tower which reaches the heavens. . . And Hashem descended to observe the city and the tower that the people had built. And Hashem said, 'Behold they are one nation that speaks one language. . . Let us descend and mix up their languages so that each one will not understand the language of his friend'" (Bereishis 11, 4 - 7). Rashi explains that Hashem said "let us" for He was including His beis din. Hashem's great humbleness prompted Him to ask permission from the angels before He carried out what He deemed as the proper course of action.
We find this exact idea in last week's parsha, too. Before creating man, Hashem said, "Let us make man in our form and image" (Bereishis 1, 26). There too, Rashi explains that it was Hashem's middah of anava that prompted Him to consult the angels. Since man would be fashioned in their form, He felt it only right to present the idea to the angels. Rashi adds that writing "let us" might cause nonbelievers to mistakenly think that there is more than one creator. Nevertheless, the Torah wished to convey that derech eretz ordains that even a great person should ask the opinion of one smaller than he.
Rav Wolbe (Shiurei Chumash) highlights the lessons to be learned from these pesukim. Firstly, Hashem could have completely ignored anyone else's interests and done as He pleased. However, He chose to ask their opinion, lest they have a bad feeling about what was going to be done. So too, any person who is in a position of authority, should not enact rules and regulations without asking the opinion of those under his dominion. Harmony reigns only when everyone understands the need for the regulation.
Elsewhere, in a slightly different vein, Rav Wolbe says that we see that a great person should ask the opinion of someone smaller than he, despite the fact that the latter's opinion will not influence the decision. Hashem would create man even if the angels would not have agreed. Nevertheless, it was an act of anava to request the permission of the angels. Additionally, we see from the pasuk that one should not attribute his actions solely to himself, rather he should say, "We" instead of "I."
The Mashgiach concludes that we should reflect for a minute on the great importance of middos tovos. In order to convey to us a lesson in derech eretz, the Torah was willing to take the risk that people would mistakenly think that Hashem was not the sole Creator of man. In light of this, a few minutes of daily mussar is definitely a worthwhile investment!