Angry Birds and Facebook were the most downloaded iPhone apps of 2011, according to Apple, but some less predictable apps also made their lists.

Craig Palli, a vice president at Fiksu, a marketing company for app developers, explained that this year's top apps incorporate three main trends: the ability to connect with friends, discovery and games that let users past the time and pick up where they left off.

The top app in the social networking category was Facebook. But Palli said the trend of connecting with friends extends further.

It also encompasses Skype, all the free texting apps and even Bump. These are all apps that lend themselves to enriching our lives through an easier and greater amount of communication and connections with friends, Palli explained.

In the music category, Pandora, which generates personalized radio stations for its users based on their music preferences, was the top app.

Pandora is such a good app that they don't really need to spend money in marketing. They just get user after user because it's such a compelling experience, Palli said.

TuneIn Radio Pro, which provides access to over 50,000 local and global stations, was another popular music app.

In the games category, Words with Friends, a multi-player game, and Angry Birds were the most downloaded apps. Games captured nine of the top ten spots on the paid apps list.

They fill those five minutes of time that we were otherwise waiting for a train or appointment, explained Palli.

He added that phones are beginning to replace cameras, which explains the success of apps in the photo and video category.

First it was the Polaroid camera, then it was the in-the-pocket digital camera. It's now just your phone.

Instagram, also named Apple's iPhone app of the year, topped the camera category. It allows users to take photos, add filters and share them with friends. Camera+, which extends the iPhone's camera with features like zoom, also made the list.

In the health and fitness category, Calorie Counter & Diet Tracker and Nike+ GPS, an app for tracking runs and workouts, were winners. But Palli said the category has fewer downloads than others.

The volume of downloads that occur in this category is less than one tenth of the other categories, he said, but he predicts that this category will grow in 2012 as people become more health-conscious and apps augment the actual device itself with something physical.

Groupon, the daily deal service, and Pimp Your Screen, which lets users customize their device with backgrounds and other visual features, were the top apps in the lifestyle category.

Netflix, the video streaming service, was the top app in the entertainment category, along with FatBooth, which lets users visualize how they might look with a few extra pounds.

Palli said free apps generally receive more downloads, and many more developers are starting to offer free versions.

During 2011, we saw a big shift in strategy from a lot of paid app developers, which was to migrate from a straight paid app experience where you pay for the app up front to an in-app purchase or upgrade experience, he explained.

This way it's really compelling for the consumer because you can get started with the app and when they experience how good the app is, they can take the wallet out of their pocket and make the extra two taps to get the full features.

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