An Olympic games, a U.S. presidential election and the end of the world are already planned for 2012, but we're more excited about the startups.

Here are six of them (in no particular order) that we expect to help define the coming year. We chose companies based on the momentum they gained in 2011, promising new takes on old problems and, in one case, the possibility of an IPO.

Did we look at every startup in the world before compiling this list? Nope. Did we overlook some of the startups speeding toward 2012 definition-dom? Yep. Which is where you come in. Let us know in the comments which startups are on your list to watch in 2012.

1. Skillshare









Skillshare is an online marketplace for offline classes. When we spoke to the startup in May, a month after it launched, more than 100 users had posted classes about everything from crocheted jewelery to how to invest your first $10,000. Eight months later, thousands of teachers have used Skillshare to teach more than 15,000 hours of classes. A few have even quit their jobs to teach Skillshare classes full-time.

While the startup began with classes clustered in New York City, it now has budding communities in San Francisco, Chicago, Boston and elsewhere. Its site interface is already set up to accommodate more than 70 U.S. and International cities. There are no or few classes offered in most of them, but by the end of 2012, we're betting there will be.

2. Zaarly, Taskrabbit or Something Similar









We're pretty sure that the mobile, local version of Craigslist will gain traction in 2012. We're just not settled on which one yet. Zaarly and TaskRabbit both allow users to find someone nearby to complete odd jobs. Zaarly also lets people request items like a reverse eBay. Both are liable to gain traction in 2012.

3. LevelUp/SCVNGR









While solutions such as Google Wallet try to introduce mobile payments through NFC technology at a time when there are few devices on the market that supports it, SCVNGR has launched a solution called LevelUp that works with any phone and any bank account. The app gives any merchant the ability to run a loyalty program that works similarly to the Starbucks App, which allows users to pay using a code displayed on their phone and collect reward points.

LevelUp users link any credit or debit card to their LevelUp accounts the same way that Starbucks links a gift card to its app. When they get to a LevelUp merchant, the app generates a unique QR code at the register that can be scanned with a merchant app to pay. Merchants can add rewards to LevelUp that are already waiting for customers the first time that they use the app, and customers earn free credit at that merchant every time they spend money there using the app.

Since launching in October, the app has signed up more than 100,000 users and has about 1,000 businesses. Meanwhile, T-Mobile has helped deploy more than 2,500 docking stations that stand in for the merchant app as a scanning mechanism at checkout counters. It's a modest start, but LevelUp has all of the ingredients to become more widespread than competing mobile payment options.

4. Dwolla









Let's be frank: transferring money through social networks sounds shady. Which is what makes it impressive that Dwolla, a payments startup that makes transfers through Twitter, Facebook, SMS and other virtual channels, was processing $1 million per day less than a year after launch.

Dwolla's 70,000 users make payments through Twitter, Facebook, SMS and other virtual channels by connecting their bank accounts to their Dwolla accounts. The service integrates with social networks to alert payment recipients there is money waiting for them in their own Dwolla accounts that can be transferred to their bank account. Payments of up to $10 are free and anything larger costs $0.25 — which is cheaper than paying a credit card fee.

In December, the company launched a new feature called Instant that lets users pay on up to $500 of credit while waiting for bank transfers from their accounts, making this process instant.

5. Eventbrite









Eventbrite is the oddball on our list of companies to watch in 2012 because the ticketing platform launched five years ago. But here are some reasons we think that 2012 is a good time to keep an eye on the startup:

It's on a growth streak. Last year it sold about 11 million tickets. This year it sold about 21 million.

It's being taken seriously by big events. This summer, for instance, it handled tickets for a Black Eyed Peas concert in New York City's Central Park in addition to 458,000 other events (more than twice as many as last year).

It's expanding internationally. Eventbrite opened a London office in October and launched localized versions of its platform in Ireland and Canada in December.

It's offline. A new iPad app lets event organizer sell tickets through Eventbrite at the door.

It could IPO. In a ZURB podcast this summer, Eventbrite CEO Kevin Hartz said that Eventbrite could file as early as 2012. "We have to continue to perform to very lofty expectations to do that," he said.

6. Codecademy









Codecademy took something that scared people, learning JavaScript, and turned it into a game. And when it's not intimidating, it turns out that learning how to code is something that a lot of people want to do. In its first 72 hours after launching this summer, Codecademy signed up 200,000 people for coding lessons. When it launched a New Years resolution class on Jan. 1, Code Year, it signed up 97,000 people in less than 48 hours to receive emails with weekly coding lessons. By the end of the week, more than 170,000 people had signed up for the class, including the Mayor.

What's interesting about Codecademy's traction is that its product is still quite limited. Lessons are restricted to JavaScript, and there isn't a clear pathway for working through the lessons. In 2012, Codecademy will expand to other coding languages, and as it does so, it will also expand its potential userbase. Thanks to Code Year, the startup will for the first time have thousands of students working on specific lessons around the same time, which could present an opportunity to add social features to the platform or create curriculum.

Image courtesy of Flickr, Gerlos, iStockphoto, kizilkayaphotos and alexsl