Ok, so the AC/DC hack doesn't quite work but it gets the desired message across.
I was scanning through my Twitter feed the other day and came upon a "Follow" that I'd forgotten about: @CiscoeBookDeal. It boils down to this: If you are on a Cisco certification track, or you value network technology texts written by certified (and battle-tested) experts for the VERY reasonable price of $USD10 then you should become familiar with this service in whatever way suits you best.
Your options are:
1. Visit this page often [http://www.ciscopress.com/deals/index.asp]
2. Subscribe via RSS in your favourite reader
3. Follow @CiscoeBookDeal on Twitter
The Twitter option, especially in my case, is fraught with danger...Well ok, not danger perhaps, just the potential to miss a great deal if you don't check in every day. For instance, right now I'm bravely typing out this message while sobbing uncontrollably at having missed the opportunity to purchase Routing TCP/IP, Volume II for $10!! You get the gist. I've now subscribed to the RSS feed as well.
The majority of the titles offered are in PDF format but, as Greg Ferro points out in this post on his blog, they are starting to convert them to other eBook formats as well.
Whatever you may think of Cisco, there are networking professionals much higher up the chain than I that keep a number of these titles as reference material. That, in itself, is recommendation enough for me. However, as an added bonus the texts are not generally completely Cisco-centric either, containing excellent general reference material.
Hope you find this useful. If you do, please pass it on so that others can benefit. Cheers.