To commemorate the pending 1 billion iPhone applications downloaded milestone, Apple revealed via iTunes the top 20 most popular paid and unpaid apps to date.

Crash Bandicoot Nitro Kart 3D and Facebook took top honors in the paid and unpaid categories respectively. Koi Pond and Enigmo rounded out the top three paid apps, while Google Earth and Pandora Radio rounded out the freebies.

The Washington Post points out some discrepancies between Apple’s top 20 and a recent comScore report. comScore claimed the free Tap Tap Revenge is the most downloaded app overall, while Apple has it ranked fourth in that category. Though, comScore was limited to PC downloads.

Apple also launched a website this weekend featuring an iPhone app download counter quickly rounding up to 1 billion. The lucky billionth downloader will receive an Apple bundle, including a 32GB iPod Touch, a MacBook Pro, and a $10,000 iTunes gift card.

More than 30,000 applications have been made available in the App Store since its launch 9 months ago.