Tbh, I find the IRS website to be quite a good read :) I've probably visited every page that's remotely retirement-related at least 100 times. If you start clicking around here and here you'll find lots of links to other useful info. The DOL/EBSA site also has some useful resources, though they're not updated as often and their site is laid out less intuitively (imo). I've also read through the relevant sections of the actual IRC and ERISA several times, but I wouldn't call those human-readable (though I learned more from those two texts than I have from anything else).
I found two main issues with using books or operational guides as a source of information:
(1) the law changes all the time, so the guides are very quickly irrelevant, and
(2) the law doesn't actually dictate HOW you have to run a retirement plan, it just tells you what requirements must be met. This leaves a lot of room for creative solutions, which is probably why you've enjoyed your job so much :)
