Free: Analog Engineer's Pocket Reference Guide
My chum Jay Dowling just emailed me to say "You should get this eBook -- it contains so much useful information -- pass this on."
The message was accompanied by this link to the Analog Engineer's Pocket Reference: Fourth Edition on the Texas Instruments' website.
(Source: Texas Instruments)
Jay is right. This pocket reference contains loads of useful information, including stuff that's of interest to everyone, even grizzled old digital design engineers, and I strongly recommend it.