This recent article by MacWorld is an excellent primer on SSL security, the underlying technologies that power HTTPS:// browsing.
This year there have been numerous reports suggesting that the fundamental security infrastructure of the Web is on shaky ground. In March we heard about a collection of stolen security certificates, and in August the release of more than 500 improperly issued certificates came to light.
It focuses on protecting Mac browsers, but talks about Windows and Google Chrome as well.