I've been reading about this stuff as much as I can also. Mostly from websites.
Here's one site that comes to mind, there's a lot of stuff there:
And this site has lots of info about various interfaces (USB, serial, parallel):
If I can remember any other good links, I'll post them. I'd like to see some other links anyone has.
Be sure to learn about the various gates (AND, OR, XOR, and their equivalent negative gates). They're just like the 6502 instructions. If you want to see what certain ICs do, once you know those you can look at it's datasheet and be able to understand what it does exactly. I've learned a lot that way.