For aesthetics, it is extremely difficult to achieve similar results to professionally made boards, although some DIYer's have done it using UV activated compounds, and exposure. Very similar to photosensitive PCB's except the coating disolves in a chemical bath when exposed to UV.
However, as previous posters have mentioned, if you just wish to protect the copper from corrosion, I have used two methods:
1. Chemical tinning solution. Clean your freshly etched board, and dip it in tinning solution, after 10-20 minutes all the copper is tinned. This not only protects the copper from corrosion, but also makes it easier to solder to. Looks pretty cool too!
2. Conformal coating lacquer: If you use the 'non acrylic' one, a light coating protects the traces from corrosion, and can be soldered through. That means you coat the entire board, pads n all, soldering melts it away, but stops it running across traces. Although I prefer tinning, this prevents all corrosion (even tinned traces oxidize after a while).
The only downside with a conformal coating is, if you wish to electrically test the board with a multimeter, the coating must be scraped/soldered away for you to get an electrical contact.
As for silk screening, on single sided boards, my preferred method is to print off the silk screen pattern onto paper, line it up, and glue it to the non-copper side of the board. Punch all the holes through with a needle, then spray with an acrylic based conformal coating... the acrylic one will not dissolve ink/toner on the paper. You end up with a shiney white board, with black 'silk screen' which, from a foot away, just looks like a white PCB.
Blueteeth