There are all sorts of new Facebook mobile apps coming out, in most cases prompted by mobile companies trying to compete against Apple’s iPhone. These apps are interesting, and some might one day be quite popular. But so far, the clearest leaders continue to be the iPhone, followed by Research in Motion’s Blackberry. That’s at least judging by what we see on our AppData service.

But before we get into those numbers, the most recent contenders come from Google’s Android operating system. Motorola recently announced a new phone, Droid, that will launch later this week and come pre-loaded with a native Facebook application. Android, unlike Apple, lets third-party applications run in the background, so you’ll be able to do things like browse Facebook from the app while listening to Pandora. Another Android app, AddressBook by Asurion, launched last week. It includes Facebook’s news feed, full profile information, status updates, notes, and many other features of the site, in a seamless interface together with Twitter, MySpace and other social sites.

There’s also the Palm Pre Facebook app that launched with the phone this spring. It has 272,000 monthly active users. There’s Nokia’s latest Facebook app, which became available with the manufacturer’s new N97 device series this fall. Among the other device-specific apps that Facebook lists on its mobile information page, the Android one has 11,000 monthly active users and the INQ one has 53,000 monthly actives, and T-Mobile’s Sidekick has 171,000. There are an unknown number on Sony Ericcson phones, Nokia phones (note the other third-party Facebook apps in Nokia’s Ovi store), and an unknown number on Windows Mobile.

Still, the only apps we know with millions of monthly active users are for the iPhone and Blackberry — and, okay, Facebook’s mobile web site, which can be accessed from any phone with a web browser. Analyzing the popularity of Facebook on mobile devices is difficult. Facebook doesn’t reveal too much about what’s happening. In early September, it said it had 65 million monthly active users — a large chunk of the 300 million users it announced at the time. Here is the other data it has recently shared: Mobile users are almost 50% more active than non-mobile users, and more than 180 operators in 60 countries are “working to deploy and promote Facebook mobile products.”

Facebook actively works with carriers to build custom version of its service; some users, for example, might get an app that lets them access some Facebook messaging features via SMS. We’ve heard that some of the recent growth in countries like Indonesia can be attributed to localized mobile apps — we’d be interested to hear more about those if readers care to share in comments, below.

There are other reasons why it’s hard to tell how popular phones for other devices are. For example, Facebook’s mobile web site uses GetJar to identify the device that the user is navigating to it on. There are currently more than 10 million monthly active users on the site, according to AppData. When the user hits the mobile page, they get a notification asking them if they want to download the app for their phone model. So whenever that service accomplishes its goal, a user disappears off into the unknown number of Facebook mobile app implementations out there. Facebook also has made Facebook Connect available for Mobile available, which is how companies like Asurion are accessing the site’s data — Connect means there are an unknown number of third-party apps for devices, developed neither by Facebook nor by device-makers and carriers.

Now, here’s the BlackBerry, coming in at 10.7 million monthly actives and 6.03 million daily active users.

Certainly, we don’t know how big Facebook is on established devices and platforms like Nokia, nor how big the Pre and Android might be one day. So, in first place is Facebook for iPhone, with 16.8 million monthly actives and 8.01 daily actives.