Hi wh,
I'm teaching an Arduino Workshop and several people just asked me that 
(I had enough Arduinos / Seeeduinos to start the class, fortunately)... Here's what I answered last night:
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There is a comparison for several Starter Sets here:
http://conductiveresistance.com/arduino-starter-kit-comparison-chart/
it does not include the Far East low-cost suppliers...
Then there's Ebay:
I' ve bought stuff from this guy, and this is a good price for a lotta stuff ...:
http://cgi.ebay.com/Arduino-DIY-Starter-Kit-lcd-Relay-Stepper-Infrared-1602-/160532624248?pt=LH_DefaultDomain_0&hash=item25607d7378
Make sure you note whether the set INCLUDES an Arduino (usually an open-source copy) or NOT.. And.. the Low-Cost Hong Kong Post shipment can take 2 weeks or so. You can pay more for faster, usually.
Then there's http://shop35392043.taobao.com/ AKA Superman.. But except for Stephen, who's from Hong Kong, you'd need to view in with Google Chrome browser with translate on.
I am trying to source this: http://item.taobao.com/item.htm?id=8807597407 which is a great price WITH an Arduino copy. I have bought Arduino Open Source copies from them, but like many Chinese businesses there are really more people and suppliers involved, and I'm not really sure yet if they are in Beijing or Shenzhen.
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It's a Big Arduino World!
In a couple of weeks my friend in Shenzhen, where I used to live, and I hope to be able to source some of this stuff.