As a newcomer to the Arduino platform, I felt that the sheer amount of Arduino ‘flavors’ (i.e. different versions) as well as Shields can be a bit confusing.  The video embedded below is my attempt to help demystify that.  I cover what the basic Arduino is, show examples of different Arduino ‘flavors’ and various shields.

As I mention in the video, the biggest factors with regard to the base Arduino flavors are:

1. 1)Physical size (do you want the standard size, which also accommodates shields, or something more compact)
   

2. 2)Computer connection:  Do you want full-size USB, Mini-USB, or “no” connection (removes the USB equipment from the board, saving space, but requires special cable)
   

3. 3)Cost & Assembly:  Some arduinos you can purchase as kits, requiring the user to assemble with a soldering iron (note: all of the kits that I have seen ONLY require through-hole soldering; no ‘smt’ or surface-mount parts, which is considerably more difficult to solder
   

4. 4)Processor heft:  are you OK with the standard Arduino, it’s memory size, speed and number of I/O or do you need more heft?
   

Shields, in my opinion, can be broken into two main categories: 

1. 1)Shields which provide different/more convenient arrangement of the Arduino pins to facilitate prototyping.  These are usually called ‘Proto’ Shields are are made by MANY different folks with different features.  Most are not assembled but only require basic soldering
   

2. 2)Shields which add Arduino functionality, including additional motor contor, wireless, ethernet, etc.
   

Here are some links which I mention in the video:

1. 1)Freeduino at NKC Electronics
   

2. 2)Illuminato, Extender shield, InputShield & More at Liquidware
   

3. 3)MakerShed (stock many different Arduino’s, including base model, Mini, Nano, Bare Bones, Boarduino, LilyPad, Motorshield, Seeduino, etc
   

4. 4)Arduino on Wikipedia (offers information on various models as they are introduced and updated)
   

5. 5)Makerbot - maker of the very cool ‘Danger Shield’ which offers multiple input sensors and is a great one-stop-shop to learning and experimenting with Arduino
   

UPDATE

Quick update/correction:

1) Arduino (the company) is actually based in Boston (i.e. USA), not Italy (although it has ties to Italy)

2) The Nano is made by Gravitech, not by Arduino.