I have long been a fan of schematics and the lack of conscious design inherent in most, the form of text instead arising from requirement and contrast with the technical illustrations. Some very interesting older documents (manuals, articles and schematics) can be found on the one electron site.

If "technical manuals" refers to in-house manuals or instruction manuals, good design often isn't the highest priority since they aren't marketing pieces. But you might look for pieces produced by companies that view design as being important (Apple, IBM, Knoll, etc.).