I saw this challenge to name as many US cities as you can posted on a blog I follow. There's no time limit - your only limit is your own persistence.
I scored 60,859,966 million people ("26.63% of the national urban population in 2010") with 201 cities before I gave up. Though if you actually want to try it with an uncontaminated slate, don't click that link or read the rest of my post until you've given up!
I was trying to think of places I've been, places with sports teams, places I've seen in TV and movies, or heard about on the news. With some cities, the challenge is spelling: It took me too long to recall that Lansing is spelled with an S.
That the game assumes a state when none is given helped. Trying to figure out a city in Vermont, I tried White Mountain, hoping there might be a city named after that mountain. There is not, but it gave me White Mountain, Alaska. (I never did recall a Vermont city, though I can't believe I failed to recall Burlington and Montpelier, despite my days rooting for Howard Dean's presidential campaign! And I failed to name either the capital or largest city of South Carolina, for the second of the two states where I failed to tally a single city.) I learned that Montclair, NJ is not a city, but got Montclair, CA out of it.
The largest city in the US that I failed to name was Nashville, Tennessee. I've never been a big country music fan. The next largest I missed was in the next state over, Louisville. Those two plus Albuquerque, NM (Go Isotopes!) round out the three cities with over 500,000 residents that I couldn't name.
The largest city I missed in California was Stockton - which is certainly a memorable sight when driving the 5 north. It somehow slipped my mind, even in the company of smaller nearby cities like Modesto and Lodi. The next largest that I overlooked was Irvine, which I've passed through uncountably many times.
The smallest city I entered was White Mountain, but again that was just by luck; the smallest I intentionally named was Industry, CA, a fiefdom with a notorious past
In Arkansas, the historically significant Little Rock eluded my memory, while the spawning grounds of mega-corp Benton did not.