One of the leading trends this year has been check-in apps. Typically mobile apps, they allow you to announce that you're at a place or doing something. The excitement started with the location check-in apps: Brightkite, Foursquare, Gowalla, Google Latitude and others. But over the past year the practice of "checking in" has expanded to many other 'things' beyond location. You can now check in to TV shows, movies, books, food, events, and more.

Below we list some example check-in apps, so that you can check out this phenomenon yourself!

Foursquare

Starting with the obvious, Foursquare has been one of the trendiest apps of 2010. For newbies who may not be familiar with it, Foursquare is a mobile app that allows you to check in to any location - cafes, sports stadiums, work places, restaurants, bars and more. Foursquare is also integrated with Twitter and Facebook, so if you wish you can publish your check-in to those services. Like many check-in apps, Foursquare offers game-like "rewards." These mostly consist of fun badges and the ability to be "mayor" of a specific place.

I use Foursquare selectively, mostly as a way to occasionally update my Facebook friends about where I am. Others use it compulsively, checking in to every single place they go to and publishing it all on Twitter and/or Facebook. We're still in the early stages of location check-ins. The rewards should get better - for example discounts at places you frequent a lot - and services like Foursquare (and perhaps the new Facebook Places) will get more useful the more that people use them.

GetGlue

GetGlue is a service where users check in to watching TV shows, reading books, listening to music - indeed, to just about anything. It has experienced strong growth this year. Founder and CEO Alex Iskold told us recently that "in the month of August alone we saw over 8 million ratings and check-ins." That's about 300,000 ratings and check-ins every day. GetGlue currently has over 600,000 users and is, according to Iskold, riding "an upward trend in the social entertainment market."

Iskold said that emotion drives a lot of the check-in behavior for GetGlue. "Which books you like, which movies you like, which shows you watch," Iskold told us, "it's self-expression and something that we'd like to discuss and tell each other about."

Shopkick

Shopkick is a check-in app for the iPhone, which launched in August. While Foursquare is more of a social tool, Shopkick is focused on monetary incentives. As ReadWriteWeb's Mike Melanson reported on the launch, "rather than rewarding users with virtual goods or contextual information like user reviews, it goes straight to the heart of the matter - kickbacks, discounts, and real-world incentives."

As Mike further explained, the idea is that everything you do earns you points, or "kickbucks," which can be redeemed for anything from Facebook Credits to gift cards. Check in to a store and get a couple of points; physically walk in and get even more points. Scan the barcodes of certain items and the points roll in. As you go, the app begins suggesting deals and offering discounts.

Shopkick launched with five big names as partners: Macy's, Best Buy, Sports Authority, American Eagle Outfitters and the Simon Property Group (an operator of malls across the country).

Foodspotting

Foodspotting is most easily described as 'Foursquare meets food.' It lets users upload photos of their favorite dishes, rate dishes and users, earn reputation points, and follow places, dishes and community members.

As we wrote in November when the service launched, the difference between Foodspotting and local business review service Yelp is that every Foodspotting review is a positive one. Instead of showcasing restaurant rants, Foodspotting offers a visual menu of customer favorites.

Tunerfish

Tunerfish is a TV-focused check-in app developed by Comcast. Like Foursquare, it makes heavy use of game mechanics. Users can earn badges for watching TV shows and "influence points," based on how many users check in after following their links.

As Marshall Kirkpatrick wrote in June, the TV industry is hoping that these kinds of applications will help it strike back against audience attrition and provide a new channel for content producers to market their work. "From a business perspective," said Comcast's social technology group senior director of product, Mike Berkley, "it's about providing awesome marketing channels for content providers. The analogy is that Foursquare (in theory) is a great marketing tool for local businesses... these TV check-in apps are a great tool for TV networks."

Tell Us Your Favorite Check-In Apps

We've listed five of our favorite check-in apps, but there are more out there that we could've mentioned. List your favorites in the comments, so that we can all check into them!