Moshe asked "Veanchnu mah? - What are we?" (Shmot 16:7). The Gemorah says he outdid Avraham in humility. Avraham referred to himself as a worm. (There's a mnemonic to remember the three great men who spoke a famous line of humility about themselves. ADA"M - Avraham, Moshe, and Dovid. Dovid referred to himself as a worm and not a man.) The usual understanding of this comparison is that it pits seeing oneself as nothing against saying you're a tiny something.
Rabbi Abraham Twerski cites a different perspective in the name of Rav Meir Shapira. Moshe was talking to people when he said he was nothing. Avraham was talking to G-d when he made his humble statement. While we don't come close to Avraham's greatness, we do all tend to be humble when we stand before G-d. It's when we deal with other humans that we feel like something special (or act that way as a defense mechanism).
Moshe's greatness was that despite his awareness of the fact that he was unique in having spoken to G-d face to face, taken the Jews out of Egypt, and received the Torah, he felt humble around other people. The people he spoke to were angry ingrates, and yet he said without sarcasm, "what are any of us?"
Rabbi Shapiro bolstered his approach with an event from the life of Rav Yonasan Eibschitz. Rav Eibschitz liked to stand to pray on Yom Kippur nearby someone who inspired him with their simple sincerity. One year at Mincha leading into Yom Kppur he overheard an elderly man paraphrasing a line from the prayers and adding with tears, "Yes, in my life I am dust, and how much more so when I die." He stayed close to that man, taking in his humility.
On Yom Kippur morning the man got an aliyah. And he shouted at the Gabbai, "Why did you give me Revi'i, and this guy got Shlishi!?! Is he more deserving of the Kavod then me?" Rav Yonason couldn't help but question the man, reminding him that yesterday he'd referred to himself as dust in this life. The reply was, "When I was praying to G-d I said I was dust because before Him that's what I am. But compared to this man - why I'm more Mechubad - worthy of honor than him!"
Perhaps the greatness of of Moshe's words lies in that it was a question. There's humility inherent in the fact that he asked about what he was, rather than declaring tha he was anything.
Moshe was open to the answer and we see that he lived his life as a something. This, despite the fact that he questioned G-d's nomination from the start.
The first (mistaken) notion that people have of humility is efacemnt of self. Denying your own worth is not humility. A more sophisticated understanding of humility is that it is knowing who you are. Great, humble men like the Chafetz Chayim and Rav Moshe Feinstein were cognizant of who they were and acted accordingly. What really rounds off the true Jewish view of humility is G-d. We gain perspective when we think of ourselves as what we are, creations of G-d. We are each a Tzelem Elokim, thus we are each great. And as much as we acheive we are all always men and not G-d, whether we speak before man or G-d.
May we be blessed with true humility.