The earliest example I saw myself was The Wild, Wild West (the 1960's TV series not the dreadful Will Smith film) but was there something before that? I've read about Adam Adamant Lives! but I've never seen that, and it was concurrent anyway.I think the best examples of steampunk can be found in visual media, as it's primarily a visual aesthetic.
I certainly agree on the visual aspect. There are even specialist shops that sell compasses and watches, and various intricately made devices; as artwork, created in a Steampunk-style, and people who collect such things, simply for their pleasing aesthetics. You see them in places like the Lanes in Brighton.
Edit: However, isn't the idea of mechanical computers, as opposed to electronic computers, also a huge element? Or, is that only the case in a small subset of Steampunk?