I didn't want to sound like I was knocking the 'Dummies' books. I've always thought they were a great reference. I really enjoy having them on my shelf at work, just for my bosses benefit. We even have a "Beginner's Guide to..." book floating around, just as a joke. But you are right, no matter what the topic has been the Dummies books are very good at easing you into a topic.
I'd also reccommend
The cramsessions are another good start.
Cisco has a CCNA prep center with some good info and video presentations (CCNA TV)
And, how can we forget tek-tips.com....without the forums, where would we be?
Something that helped myself and another co-worker as we were studying, was a chart that our boss showed us and we expanded on. He had the diagonal row and the first row across, we added too it.
| 255|
| 254| |
| 252| | |
| 248| | | |
| 240| | | | |
| 224| | | | | |
| 192 | | | | | | |
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
| 2^7 | 2^6 | 2^5| 2^4| 2^3| 2^2| 2^1| 2^0|
| /25 | /26 | /27| /28| /29| /30| /31| /32|
The diagonal row would be the decimal value for the subnet mask.
The first row across is the value for each bit for the octet.
The second row across is the powers of 2.
The third row is the prefix notation.
Since you want to be able to do subnetting in a flash, this saved me a bunch of time. I've gone so far as to put this in a spreadsheet and have posted on my wall just for general reference. Just today updated it so it has all four octets displayed. Happy to send it to anyone that wants it....