DISCLAIMER: About to mention stuff from my own shop...
I have looked in detail at all the starter sets I could find, and bought several. After all that my friend and I developed these:http://arduino-direct.com/sunshop/index.php?l=product_list&c=6
One problem is that the nice boxes are expensive to ship. I'm thinking of making the same kits available in bulk pack, and get you own box at walmart or Home Depot or HarborFreight??
We also make up kits for schools and universities, including open-source copies of Arduinos, at a low cost. I'm thinking of making those available as a real low-cost starter kit, no frills.. We do have a lot of How-To on our Info site: http://arduino-info.wikispaces.com
And for a quick start for newbies: http://arduino-info.wikispaces.com/GettingStarted-Software
And there is a big question about newbies starting with breadboards or easy-to-connect options like: http://arduino-info.wikispaces.com/BrickStarterSet
I love these Electronic Bricks and the combination of the Sensor Shields (http://arduino-info.wikispaces.com/SensorShield
and cables that make it easy to make secure connections: http://arduino-info.wikispaces.com/Cables
These are particularly good for classes where you don't want to spend half the class time debugging breadboard connections.
Anyway, these are just my thoughts. I agree that getting a good collection of interesting sensors is a great start. But some just don't know WHERE to start.
Any suggestions for products or online How-To you'd like to see would be appreciated...
Regards, Terry King
...On the Mediterranean in Italyterry@yourduino.com