Here’s my list of favourites in descending order:

• Google Skymap: Here’s a cute little app. It’s essential if you’re into astronomy, but if, like me you have just a passing curiosity, it’s still a lot of fun. It shows you a map pointing out the brightest naked-eye stars, planets, sun and moon, constellation lines, horizon, cardinal points, and Messier Objects. The awesome part though, is that it uses the phone’s GPS, accelerometer and compass to figure out where you are, where you are pointing your phone and therefore which part of the sky you’re looking at. It therefore shows you the night sky you’re looking at and helps you identify all the different objects you’re looking at.
  
  

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• Twidroid: An awesome Twitter client that does everything you may want from a Twitter client and then some. It can use your phone’s GPS or other location-based services to automatically post your location and the phone’s camera to snap and upload photos right to yourTwitter account. It does all the great things the best Twitter clients do, lets you retweet things efficiently, reply to tweets and DM people really easily. If you’re a Twitter fiend, it’s very much recommended.
  
  

  Read more about Twidroid.

• Shazam: Ever seen an application that looks just like magic? Well Shazam is one of those. Let’s say you’re sitting in the car and a great song comes on the radio. Don’t you hate it when the song finishes and you never learn what it was? Well, with Shazam, all you do if fire up the app, let it listen to a few seconds on your song and bang, it comes back with the name of the song, the artist and all the information you could ever want to learn about it.
  
  

  Read more about Shazam.

• Shopsavvy: Here’s another interesting application. It lets you scan a barcode on a book and tells you what the book is, giving you quick access to reviews about it. Big deal you might say; but there’s also another aspect to it. It looks for the book online and tells you what the prices are from a number of different online retailers; so if you’re in a bookstore, you can immediately tell if you have a good deal or not. But wait, there’s another twist. Using location-based services it also does a check of other book retailers in the area and check what they’re selling the book at. So, if the shop you’re checking the price in is too expensive, you can just nip next door and get it from the cheaper place.
  
  

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• Wikitude: This is just the most awesome application ever. Imagine you’re driving along and see a building on the horizon. You have no idea what it is. Well, Wikitude checks where you are, pings Wikipedia pulling down landmarks in the area, and uses the compass and camera in your phone to superimpose the inforamtion on the image you’re looking at. It’s a type of technology called Augmented Reality and you have to see it to realise just how awesome it it.
  
  

  Read more about Wikitude

These are just five of the applications I have tried so far. There are others out there that I haven’t got to yet, one particular area I’m interested in is live video streaming services, but I just haven’t managed to find anything that works for me yet. I also have a number of games that are going into a similar post to this, that is .. when I get round to posting it. There’s some amazing stuff in there, so if you have an Android phone and haven’t seen one of the five above, just pop onto the Market and give them a try. They’re all free!