Update: Between the writing and publishing of this entry, Ngmoco blew up.  First came the rumors, then the facts. That’s $400 Million worth of proof that Free-to-Play apps have a huge future on the Apple App Store!

Looking for a measure of how much impact Free-to-Play games are making on the Apple App Store? As Finger Gaming noted last week, free apps occupied 5 of the top 10 iPad top Grossing spots. And last Friday afternoon around 4:30pm PST, 12 of the Top 50 Highest Grossing iPhone Games were free. This is not a huge shock, given the runaway success companies like Zynga and the artist formerly known as Playdom are seeing with the free model on Facebook and MySpace. But it is great to see free apps successfully competing against branded juggernauts such as Madden, FIFA, Bejeweled and Final Fantasy in the Apple App Store.

Check out the list of free titles in the Top 50 Grossing iPhone Game Apps (10/01/2010 at 4:30PM PST):

CityStory TeamLava
We Rule Ngmoco
Haypi Kingdom Haypi
Zombie Farm Playforge
Coin Push Frenzy Freeverse
Original Gangstaz Rock Addmired
Millionaire City Digital Chocolate
Tap Fish BayView Labs
We City Ngmoco
Farm Story TeamLava
We Farm Ngmoco
Pocket Frogs NimbleBit

Several interesting notes about the titles on this list:

farmVille FarmVille was not in the Top 50 when this snapshot was taken. However, it was in the Top 5 earlier Friday. Free apps seem to be among the more migratory apps on the Highest Grossing list. This makes sense because revenue is generated on the audience buying in-game items, not initial downloads. Standard Pay-to-Download apps should see more steady revenue, as downloads are based on deck placement (Top Sellers, Apple feature), which is usually more stable within a day. The ebbs and flows of the in-game purchases will average out to a certain $ per DAU over longer time frames, but there will be tremendous fluctuation within a thin slice of a time period.
ngmoco Ngmoco is represented 3 times on this list; 4 times if you count the Freeverse title. Ngmoco publicly committed to the Free-to-Play model early this year and their early position seems to have paid off in a sizable audience.
MillionaireCity Millionaire City is the only iPhone app on this list that also has an app on Facebook. Given Dchoc’s pedigree in mobile combined with their strong presence in Facebook, it is unsurprising to see them among the leaders in cross-platform Free apps. With just over 9 Million MAU on the Facebook version, Millionaire City has the potential for a long life as a Top Grosser.
Coinpush Coin Push Frenzy and Haypi Kingdom stand out as having very different game mechanics from the rest of the list. Coin Push Frenzy takes the Arcade classic coin pushing game and monetizes it. Haypi Kingdom is a MMORPG. All of the other games are in the same vein as successful Facebook apps (tending to Farms, animals, cities or having gang wars).

An abundance of free apps in the App Store top grossing list is great news for all app publishers. It proves that the downward pressure on app prices does not need to lead to an erosion of revenue for publishers. Free with in-game monetization can lead to significantly more revenue than a $.99 price point. In my opinion, this is just the beginning of the Free invasion of the App Store top grossing list. The Facebook apps (FarmVille, Millionaire City, Mafia Wars) and their ilk will make more noise in the upcoming months. Beyond that, apps that push the in-game purchase envelope to different types of gameplay have huge potential to generate revenue. Because of their ability to activate social graphs (via FB Connect, Game Center, etc.) and spread virally, Free apps with multiple revenue streams have a very bright future.